King Afonso V of Portugal grants Lisbon merchant Fernão Gomes the monopoly of trade in the Gulf of Guinea in 1469.

Besides the payment of an annual rent of two hundred thousand reais, Gomes is to explore one hundred leagues of the coast of Africa per year, for five years (the agreement is later extended for another year).

He also receives a monopoly of trade in guinea pepper for another yearly payment of one hundred thousand reais. (At this time called "malagueta", it is a popular substitute for black pepper.)

Gomes employs explorers João de Santarém, Pêro Escobar, Lopo Gonçalves, Fernão do Pó and Pedro de Sintra, He exceeds the requirements of his grant: his expeditions reach the Cape of Santa Catarina, already in the Southern Hemisphere, and also the islands of the Gulf of Guinea.

In 1471, they reach Elmina (meaning "the Mine"), where they find a thriving alluvial gold trade.

Pêro Escobar helps to discover the gold industry that will grow around this first European settlement in West Africa.

Prior to the arrival of the Portuguese, the town was called Anomansah (the perpetual drink).

Near the coast at Elmina is fought a large battle in 1478, during the War of the Castilian Succession, between a Castilian armada of thirty-five caravels and a Portuguese fleet for hegemony of the Guinea trade (gold, slaves, ivory and melegueta pepper).

The war ends with a Portuguese naval victory followed by the official recognition by the Catholic Monarchs of Portuguese sovereignty over most of the West African territories in dispute embodied in the Treaty of Alcáçovas, 1479.

This is the first colonial war among European powers.

Many more will follow.

The War of the Castilian Succession (1475–1479) and the Treaty of Alcáçovas

The War of the Castilian Succession (1475–1479) was a dynastic and international conflict fought between the supporters of Joanna la Beltraneja, daughter of Henry IV of Castile, and those of Isabella of Castile, Henry IV’s half-sister. This war determined the future of Iberian unification and colonial expansion.

Key Players and Their Alliances

• Isabella of Castile (married to Ferdinand of Aragon)
  • Supported by Aragon, seeking to consolidate Spanish unity.
  • Opposed by France, which was a rival of Aragon for control in Italy and Roussillon.
• Joanna la Beltraneja (married to her uncle, King Afonso V of Portugal)
  • Supported by Portugal, which aimed to maintain Castilian independence and retain influence.
  • Backed by France, in opposition to Aragon’s expansion.

Military and Naval Engagements

• Despite initial victories for Joanna’s faction, Afonso V of Portugal failed to act decisively, allowing Isabella to consolidate power.
• The Battle of Toro (1476), though inconclusive, favored Isabella politically, leading to her recognition as Queen of Castile in the Cortes of Madrigal-Segovia (1476).
• The war shifted focus to naval warfare, particularly over control of Atlantic trade routes.
• In 1478, the Portuguese navy won a decisive victory at the Battle of Guinea, securing access to gold and slaves in West Africa.

The Treaty of Alcáçovas (1479): Defining Iberian and Colonial Power

• The treaty recognized Isabella and Ferdinand as sovereigns of Castile, ending Portuguese claims to the throne.
• Portugal, in return, gained exclusive control over the Atlantic trade, except for the Canary Islands, which remained Castilian.
• The treaty formally established Portugal’s hegemony in maritime exploration, securing:
  • The Azores, Madeira, and Cape Verde.
  • Exclusive rights to trade in West Africa and its gold and slave markets.
• Joanna la Beltraneja lost all claims to the Castilian throne, living the rest of her life in Portugal.

Impact on Colonialism: The Division of the World into Spheres of Influence

• The Treaty of Alcáçovas set a precedent for European colonial expansion, formally dividing newly discovered lands without considering indigenous peoples.
• This principle was further codified in the Treaty of Tordesillas (1494), dividing the New World between Spain and Portugal.
• The same ideology of dividing the world into European spheres of control persisted for centuries, culminating in the Berlin Conference (1884–1885), which partitioned Africa among European colonial powers.

Conclusion: The Treaty’s Lasting Legacy

• The War of the Castilian Succession secured Spanish unification and Portugal’s dominance in Atlantic exploration.
• The Treaty of Alcáçovas established the European precedent for colonialism, shaping the future of global imperialism.
• This principle of "spheres of influence" became an accepted norm in European diplomacy, influencing colonial treaties up to the 20th century.

The war and its aftermath reshaped Iberia, global trade, and European geopolitics, setting the stage for the Age of Exploration and the colonial empires that followed.

Atlantic Southwest Europe: Struggles for Succession and Maritime Triumphs (1468–1479)

From 1468 to 1479, Atlantic Southwest Europe witnessed significant political upheaval driven by dynastic conflicts in Castile, consolidation of royal power in Portugal, and persistent internal disputes within Navarre. Simultaneously, maritime achievements further solidified Portugal’s status as an emerging global naval and commercial power.

Political and Military Developments

• Portugal: King Afonso V (r. 1438–1481) intensified military efforts in Morocco, culminating in the capture of Arzila and Tangier in 1471, solidifying Portugal’s foothold in North Africa and positioning it as a prominent Atlantic maritime power. Domestically, the Portuguese monarchy enjoyed relative stability, reinforcing royal authority and centralization that laid groundwork for future maritime exploration under his son João, who became increasingly influential in policy.
• Northern Castile and León: The contentious succession struggle escalated dramatically following the death of Enrique IV (1474). His daughter, Joanna la Beltraneja, supported by Portugal’s Afonso V, contested the throne against Enrique’s half-sister, Isabella of Castile, sparking the destructive War of the Castilian Succession (1475–1479). The Basque territories, Galicia, and northern Rioja were severely impacted by the conflict, with local nobles divided in allegiance, leading to intermittent warfare and economic disruption.
• Navarre: Navarre endured ongoing instability under Leonor I (1479), whose brief reign reflected continuing succession crises and foreign interference, particularly from neighboring Castile and Aragon, exacerbating internal divisions and undermining effective governance. Persistent political uncertainty deepened Navarre's vulnerability, making it increasingly susceptible to external manipulation.

Economic and Maritime Expansion

• Portuguese Maritime Success: Portugal’s capture of key Moroccan port cities in 1471 significantly boosted trade in gold, ivory, spices, and slaves, enriching Lisbon as a critical European economic hub and stimulating merchant wealth and international commerce. Advances in navigation continued, with improved cartographic knowledge and ship design further enabling Portugal’s pioneering role in European exploration of the Atlantic and African coasts.
• Economic Disruptions in Northern Iberia: In Castile, particularly northern regions including Basque ports and Galicia, commerce and agriculture suffered from the prolonged civil war, although the robust maritime trade in wool and iron persisted despite disruptions, due to well-established northern trading networks. Navarre’s internal turmoil negatively impacted local trade, weakening the region’s commercial stability, though its strategic location kept it involved in broader European trade routes.

Cultural and Social Developments

• Portuguese Courtly Culture: Lisbon's royal court continued patronizing intellectual pursuits, fostering Renaissance humanism and attracting prominent scholars and artists, elevating Portugal’s cultural prestige within Europe. Chroniclers like Gomes Eanes de Zurara actively documented Portuguese maritime conquests, contributing significantly to Europe’s collective knowledge of Africa and the wider Atlantic world.
• Cultural Identity Amidst Conflict: Despite political instability, the Basque Country and Galicia strengthened their local identities, preserving distinct legal traditions (fueros) and language amid centralizing pressures from Castile’s emerging monarchy. Pilgrimage routes, particularly to Santiago de Compostela, remained vibrant conduits for cultural and scholarly exchanges despite disruptions from military conflicts.

Significance and Legacy

The era 1468–1479 decisively shaped the future of Atlantic Southwest Europe. Portugal's military successes cemented its reputation as a preeminent maritime empire, while Castile's dynastic conflicts resolved in favor of Isabella, whose victory set the foundation for unified Spanish monarchy. Navarre’s political fragility highlighted broader Iberian power dynamics, foreshadowing its later absorption by neighboring powers. Economically, culturally, and politically, these developments profoundly influenced subsequent regional histories, driving Portugal toward global expansion and setting the stage for Spain's consolidation as a unified kingdom.

Atlantic Southwest Europe (1468–1479 CE): Portuguese Expansion and Cultural Renaissance, Castilian Political Unification under Isabella and Ferdinand, and Navarrese Diplomatic Realignment

Between 1468 and 1479 CE, Atlantic Southwest Europe—including Galicia, northern and central Portugal, Asturias, Cantabria, and northern Spain south of the Franco-Spanish border (43.05548° N, 1.22924° W)—underwent a significant transition. Portugal further consolidated its global maritime empire and cultural renaissance under King Afonso V, Castile moved decisively toward political stabilization and unification through the marriage of Isabella I of Castile and Ferdinand II of Aragón, and Navarre navigated diplomatic realignments under John II of Aragón. This period crucially set the stage for the mature Iberian Renaissance, profound geopolitical transformations, and expansive maritime achievements in the coming decades.

Political and Military Developments

Portuguese Maritime Empire under Afonso V

Portugal continued its ambitious maritime and colonial expansion under the energetic leadership of King Afonso V (1438–1481 CE). Portuguese explorers systematically charted Africa’s coastline, securing significant footholds in West Africa, including São Tomé (1471). Portugal decisively cemented its position as Europe’s premier maritime and trading power, underpinning economic prosperity and cultural flourishing.

Castilian Political Unification and Stability

In Castile, the decisive marriage between Isabella I of Castile and Ferdinand II of Aragón (1469 CE) fundamentally reshaped the Iberian political landscape. This marriage, combined with Isabella’s assertive governance following the resolution of civil strife after Henry IV’s death (1474 CE), decisively restored Castilian internal stability and reinforced royal authority. The subsequent War of the Castilian Succession (1475–1479 CE) was resolved with the Treaty of Alcáçovas (1479 CE), securing Isabella’s rule, stabilizing Castilian governance, and providing foundations for future political centralization and Renaissance cultural revival.

Navarrese Diplomatic Realignment

Navarre, under the later rule of John II of Aragón (1425–1479 CE), navigated complex diplomatic realignments amid broader Iberian political upheavals. John II successfully managed Navarrese territorial integrity and internal coherence, despite succession disputes involving his children. His diplomatic pragmatism significantly preserved Navarre’s regional autonomy and geopolitical stability through careful management of Castilian and French influences until his death in 1479.

Economic Developments

Agricultural Prosperity and Economic Stability

The region maintained robust agricultural productivity and economic stability through diversified cultivation—including grain, vineyards, olives, citrus fruits, almonds—and sustained livestock production. Gold and silver mining in Galicia and Asturias decisively reinforced economic resilience, demographic stability, and regional prosperity.

Portuguese Maritime Dominance and Global Commerce

Portuguese maritime trade decisively flourished through major ports such as Lisbon, Porto, Braga, and Coimbra. Trade with West Africa, northern Europe (England, Flanders, Normandy, Brittany), and the newly explored Atlantic islands significantly expanded, reinforcing Portugal’s economic dominance and maritime influence. Galicia, particularly through ports such as A Coruña, maintained strong trade activity, reinforcing regional economic resilience.

Pilgrimage Economy and Cultural Exchange in Galicia

Pilgrimage routes to Santiago de Compostela decisively continued to support regional economic vitality, hospitality industries, artisanal trade, infrastructure projects, and cultural exchanges. Persistent pilgrimage significantly reinforced Galicia’s economic stability, cultural prominence, and international recognition.

Cultural and Religious Developments

Portuguese Renaissance Cultural Flourishing

Portugal experienced a decisive cultural flourishing through humanist scholarship, literary patronage, artistic innovation, and scientific inquiry under King Afonso V. Robust cultural exchanges with Italy and northern Europe deepened Renaissance influences, significantly enhancing Portuguese intellectual, artistic, and educational life, notably reflected in expanding royal libraries, advanced cartography, maritime scholarship, and early colonial administrative writings.

Castilian Cultural Renewal and Early Humanist Scholarship

Castilian culture decisively experienced a revival under Isabella and Ferdinand, enriched by growing Renaissance humanist influences from Italy and broader Europe. Intellectual exchanges intensified, fostering literary, philosophical, educational, and artistic advancements, notably shaping Castile’s nascent Renaissance identity and reinforcing the prestige of Castilian courtly culture.

Galician Cultural Resilience and Ecclesiastical Patronage

Galicia maintained significant cultural prominence, decisively supported by ecclesiastical institutions of Santiago de Compostela and monastic communities. Scholarly initiatives, manuscript preservation, artistic patronage, and architectural projects continued, reinforcing Galicia’s cultural identity and international visibility.

Persistent Cultural Syncretism and Local Traditions

Orthodox Christianity consistently integrated indigenous Iberian and Celtic traditions, particularly in rural Galicia and northern Portugal. Persistent cultural syncretism decisively reinforced regional identities, social cohesion, and cultural resilience during this transformative era.

Civic Identity and Governance

Portuguese Civic Unity and Global Ambitions

Portugal decisively reinforced civic unity, national identity, and stable governance under King Afonso V. Maritime exploration significantly shaped Portuguese collective ambitions, laying critical foundations for global empire-building, economic prosperity, and cultural flourishing.

Castilian Civic Identity and Political Unification

Castile decisively restored civic unity, territorial integrity, and governance stability following Isabella and Ferdinand’s union, successfully overcoming earlier aristocratic conflicts. The resulting political unification profoundly influenced Castilian regional identity, administrative centralization, and intellectual and cultural renewal.

Navarrese Regional Autonomy and Diplomatic Stability

Navarre decisively preserved regional autonomy, diplomatic neutrality, and internal governance coherence under John II of Aragón. His diplomatic pragmatism significantly maintained territorial integrity, regional stability, and northern Iberian geopolitical coherence.

Notable Regional Groups and Settlements

• Portuguese: Experienced decisive global maritime expansion, economic prosperity, and cultural renaissance under Afonso V, significantly shaping Portugal’s historical trajectory and future global influence.

• Castilians: Restored decisive governance stability, territorial integrity, and cultural renewal under Isabella I and Ferdinand II, significantly influencing Iberian political, intellectual, and cultural developments.

• Galicians: Sustained vibrant economic resilience, cultural vitality, and ecclesiastical prominence, significantly reinforced by pilgrimage activity and maritime commerce.

• Basques (Navarre): Maintained regional autonomy, diplomatic neutrality, and stable governance under John II of Aragón, significantly shaping northern Iberian political coherence.

Long-Term Significance and Legacy

Between 1468 and 1479 CE, Atlantic Southwest Europe:

• Achieved decisive Portuguese maritime dominance, economic expansion, and Renaissance cultural flourishing, decisively setting foundations for Portugal’s subsequent global empire and cultural prominence.

• Experienced fundamental Castilian political unification and governance stabilization under Isabella and Ferdinand, significantly influencing Iberian political consolidation and cultural renewal, laying key foundations for the Spanish Renaissance.

• Navigated Navarrese diplomatic complexity, territorial autonomy, and governance stability under John II of Aragón, significantly influencing northern Iberian geopolitical coherence.

• Maintained resilient agricultural prosperity, expanding maritime commerce, pilgrimage-driven economic stability, and vibrant cultural renewal, profoundly shaping regional historical trajectories.

This transformative era decisively shaped regional identities, governance structures, economic continuity, cultural resilience, and intellectual foundations, profoundly influencing Atlantic Southwest Europe’s trajectory toward the full flowering of the Iberian Renaissance and setting the stage for significant global impacts in subsequent centuries.

Isabella and her husband Ferdinand of Aragon jointly succeed to the Castilian throne upon the death of her half brother, King Henry IV of Castile and León, in late 1474, despite the prior swearing-in of Henry’s alleged daughter and heir, the now-twelve-year-old Joanna la Beltraneja of Portugal.

Isabella and Ferdinand, under an agreement made between the royal couple and a noble-cleric group, are crowned joint sovereigns of Castile and León on December 13, 1474.

The royal pair, who will become known as the “Catholic kings,” are exceptionally gifted: she in internal politics and Ferdinand in foreign policy.

The Struggle for Ciudad Real in the Castilian Succession War (1475–1476)

During the War of the Castilian Succession (1475–1479), Ciudad Real, a strategic city in La Mancha, changed hands multiple times between the rival factions of Joanna la Beltraneja (supported by Portugal) and Isabella of Castile. The battle for the city reflected the broader struggle between Portugal and Castile over control of central Spain.

Rodrigo Téllez-Girón Captures Ciudad Real for Joanna

• Rodrigo Téllez-Girón, Master of the Order of Calatrava, was a staunch supporter of Joanna la Beltranejaand her Portuguese backers.
• As the leader of a powerful military-religious order, he launched an offensive into La Mancha, a critical frontier region.
• He successfully captured Ciudad Real, securing an important stronghold for Joanna’s faction.

Rodrigo Manrique Recaptures Ciudad Real for Isabella

• Rodrigo Manrique, treasurer of the Order of Calatrava and Master of the Order of Santiago, was a loyalist of Isabella and Ferdinand.
• Recognizing the strategic importance of Ciudad Real, he led an Isabelline counteroffensive to reclaim the city.
• His forces recaptured Ciudad Real, reinforcing Isabella’s control over central Castile and weakening Portuguese influence in the region.

The Importance of the Battle for Ciudad Real

• La Mancha was a crucial battleground between the rival claimants, as it provided a strategic link between northern and southern Castile.
• The city’s final capture by Isabella’s forces helped consolidate her hold over Castile, while Afonso V of Portugal’s support for Joanna weakened.
• This shift in momentum ultimately led to Isabella’s triumph, culminating in the Treaty of Alcáçovas (1479), which ended the war and confirmed her as Queen of Castile.

The fall and recapture of Ciudad Real was a key moment in the Castilian Succession War, demonstrating the power struggle between the Iberian military orders and the rival monarchs vying for the Castilian throne.

Isabelline Counteroffensive: The Fall of Trujillo and the Securing of Strategic Castilian Lands (Late 1475–1476)

As the War of the Castilian Succession (1475–1479) progressed, Isabella I of Castile and her supporters launched a major counteroffensive, seizing key territories that had previously backed Joanna la Beltraneja and her Portuguese allies.

The Capture of Trujillo and the Securing of Military Orders’ Lands

• In late 1475–early 1476, Isabelline forces launched a successful campaign against Portuguese and pro-Joanna positions.
• Trujillo, a vital city in Extremadura, was captured by Isabella’s supporters, cutting off Portuguese access to central Castile.
• Isabella’s forces also gained control of key military order territories, which had previously supported Joanna:
  • A significant portion of the Order of Calatrava's lands—weakening a major ally of Joanna.
  • The lands of the Order of Alcántara, further eroding Portuguese influence in Castile.
• Additionally, Isabella’s supporters secured the Marquisate of Villena, a large and strategically important domain in eastern Castile, further tilting the war in her favor.

Impact on the War

1. Weakened Joanna’s Support Base – With the loss of Trujillo and military order lands, Joanna and Afonso V were left with fewer Castilian allies.
2. Strengthened Isabella’s Position – Gaining control over the orders of Calatrava and Alcántara reinforced Isabella’s claim to the throne, as these orders had substantial military and political power.
3. Strategic Blow to Portugal – Afonso V’s forces were now increasingly isolated, with dwindling options for maneuvering in Castile.

A Turning Point Leading to the Battle of Toro (1476)

• The fall of Trujillo and other territories weakened the Portuguese position in Castile, setting the stage for the decisive Battle of Toro (March 1, 1476).
• Though the battle itself was militarily indecisive, Isabella’s political advantage grew, leading to the eventual collapse of the Portuguese campaign and the signing of the Treaty of Alcáçovas (1479).

The Isabelline counteroffensive, particularly the capture of Trujillo and control over military orders’ lands, was a turning point in the war, accelerating Joanna’s decline and Isabella’s final victory.

The Castilian Succession Crisis: Afonso V’s Invasion and Marriage to Joanna la Beltraneja (1475)

Following the death of King Henry IV of Castile and León in 1474, a succession crisis erupted between two rival claimants:

1. Joanna la Beltraneja – Henry IV’s alleged daughter, supported by Portugal and a faction of Castilian nobles.
2. Princess Isabella of Castile – Henry IV’s half-sister, supported by her husband, Ferdinand of Aragon, and a rival faction of Castilian nobility.

The conflict led to the War of the Castilian Succession (1475–1479), a decisive struggle between Portugal and Castile, with France and Aragon also involved.

Afonso V’s Invasion of Castile and His Marriage to Joanna (1475)

• On May 10, 1475, King Afonso V of Portugal led an army into Castilian territory, launching an offensive to claim the Castilian throne.
• He advanced to Plasencia, where Joanna la Beltraneja awaited him.
• On May 25, 1475, Joanna and Afonso were proclaimed sovereigns of Castile, asserting their right to rule as king and queen.
• To strengthen his claim, Afonso married Joanna, despite being her uncle, making a Papal dispensation necessary.
• The required papal approval was granted several months later, reinforcing their legitimacy in the eyes of their supporters.

Consequences and the Prolonged Succession War

• Isabella and Ferdinand rejected the union, leading to full-scale war between Portugal and Castile-Aragon.
• The war lasted until 1479, with naval and land battles fought over the Castilian crown and Atlantic trade routes.
• Afonso’s lack of military aggressiveness and the stalemate at the Battle of Toro (1476) weakened Joanna’s claim.
• The war ended with the Treaty of Alcáçovas (1479), which:
  • Recognized Isabella and Ferdinand as rulers of Castile.
  • Confirmed Portugal’s dominance in the Atlantic, except for the Canary Islands.
  • Forced Joanna to renounce her claim and retreat to a convent in Portugal.

The failed campaign marked Portugal’s last attempt to unite with Castile, while Isabella and Ferdinand’s victory paved the way for the unification of Spain and their global expansion.

The Portuguese Advance in the Castilian Succession War (1475)

After Afonso V of Portugal and Joanna la Beltraneja were proclaimed sovereigns of Castile in Plasencia on May 25, 1475, the Portuguese army marched towards Arévalo, intending to continue toward Burgos, a strategic city in the conflict.

Strategic Importance of Burgos

• Afonso V hoped to unite with troops sent by his ally, Louis XI of France, reinforcing his army against Isabella and Ferdinand.
• However, Burgos was divided:
  • The castle of Burgos was held by the Estúñiga family, who supported Joanna la Beltraneja.
  • The city itself was controlled by the Fernández de Velasco family, loyal to Isabella of Castile.

Portuguese Strategy and Challenges

• Afonso’s next move depended on securing support from Castilian noble factions, particularly in Burgos, which was a vital stronghold.
• Despite the loyalty of the Estúñigas, the Portuguese advance faced resistance from Isabella’s supporters.

Outcome: Afonso’s Difficulties in Securing Castilian Support

• The war did not unfold as Afonso V had expected. His military movements were slow, and Castilian nobles who had initially supported Joanna became increasingly hesitant.
• This hesitation, combined with Isabella’s consolidation of power in key cities, made it difficult for Afonso to sustain his campaign.

The struggle for Burgos and northern Castile was part of the broader War of the Castilian Succession (1475–1479), which ultimately resulted in Isabella and Ferdinand’s triumph, while Afonso failed to secure Castile for Joanna.

Afonso V’s Strategic Shift: Consolidating Control in Toro (1475)

After marching from Plasencia to Arévalo in May 1475, Afonso V of Portugal encountered less Castilian support than he had anticipated in his campaign for the Castilian throne. Realizing that his position in Castile was weaker than expected, he abandoned his plan to march toward Burgos and instead focused on securing areas closer to Portugal.

Strategic Decision: The Shift to Toro

• Instead of advancing further into Castile, Afonso V redirected his efforts toward consolidating control over Toro, a key city near the Portuguese border.
• Toro received Afonso favorably, offering him a strong base of operations.
• However, while the city welcomed him, the castle garrison remained loyal to Isabella, highlighting the deep divisions within Castile.

Why Toro Was a Strategic Choice

1. Proximity to Portugal

   • Securing Toro allowed Afonso to maintain supply lines from Portugal and ensure he could retreat if necessary.

2. Symbolic and Political Importance

   • Toro was a historically significant Castilian city and had a strong noble presence.
   • By holding Toro, Afonso could demonstrate legitimacy and encourage more Castilian nobles to join his cause.

3. Tactical Positioning Against Isabella

   • Controlling Toro allowed Afonso to prepare for battle, as Isabella and Ferdinand were mobilizing their forces.

Consequences of Afonso’s Decision

• Afonso’s failure to push further into Castile weakened his overall campaign.
• The decision to focus on Toro led to the Battle of Toro (1476), a crucial and inconclusive battle in which both sides claimed victory.
• Although Afonso held Toro after the battle, Isabella’s political position grew stronger, leading to her eventual recognition as Queen of Castile.

Conclusion: Afonso’s Missed Opportunity

• Afonso’s reliance on Portuguese forces and lack of widespread Castilian support made his campaign difficult.
• By failing to secure Burgos and northern Castile, he lost the chance to challenge Isabella more effectively.
• His retreat to Toro set the stage for the eventual collapse of his claim to the Castilian throne, culminating in the Treaty of Alcáçovas (1479), which confirmed Isabella’s rule and Portugal’s dominance in the Atlantic.