The Flemish Succession Crisis and the Rise of Thierry of Alsace (1127–1128 CE)

Following the assassination of Count Charles the Good in 1127, Thierry of Alsace laid claim to the County of Flanders as the grandson of Robert I of Flanders. However, his rival William Clito, the son of Robert Curthose and grandson of William the Conqueror, was installed as Count of Flanders with the backing of King Louis VI of France.

Despite William Clito’s Capetian support, his rule quickly became unpopular, as his policies threatened the autonomy of Flanders. By the end of 1127, major Flemish cities, including Bruges, Ghent, Lille, and Saint-Omer, had declared their support for Thierry, escalating the conflict into a full-fledged succession war.

Early Battles and Thierry’s Struggles (1127–1128)

• Thierry’s support came primarily from the Imperial faction in Flanders, aligning himself with Emperor Lothair II rather than the Capetians.
• Upon arriving in Flanders, Thierry immediately engaged William Clito in battle, seeking to secure control over the contested county.
• In retaliation, Louis VI of France had Thierry excommunicated by Archbishop Raymond of Martigné of Reims, branding him a rebel against Capetian rule.
• Louis VI then personally besieged Lille, attempting to crush Thierry’s rebellion, but was forced to withdrawwhen King Henry I of England, William’s uncle, switched his support to Thierry.

Despite these victories, Thierry suffered major defeats at Tielt and Oostkamp, forcing him to retreat to Bruges, his main stronghold. When Bruges also became untenable, he fled to Aalst, where he was soon besieged by William Clito, Godfrey I of Leuven, and Louis VI.

The Sudden Death of William Clito (July 27, 1128)

• With Aalst on the verge of capture, Thierry’s prospects seemed bleak, and it appeared that Capetian control over Flanders was imminent.
• However, William Clito suddenly died on July 27, 1128, reportedly from a wound sustained during the siege.
• His unexpected death left Thierry as the only remaining viable claimant to the county.

Thierry of Alsace Becomes Count of Flanders

With William Clito gone, Capetian ambitions in Flanders collapsed. Thierry was able to secure control over the county, establishing his rule as Count of Flanders and ending the Capetian-backed resistance.

Significance of the Flemish Succession War

• Thierry’s victory reinforced Flemish autonomy, ensuring that Flanders remained independent from direct Capetian rule.
• Louis VI’s attempt to expand Capetian influence into Flanders had failed, marking a setback for Capetian ambitions in northern France.
• Henry I of England’s intervention proved decisive, further demonstrating the ongoing Anglo-French rivalry over influence in Flanders and Normandy.
• Thierry’s long reign (1128–1168) would see Flanders emerge as a powerful economic and political force in medieval Europe, playing a crucial role in the trade networks of the North Sea and the Low Countries.

The Flemish succession crisis (1127–1128) had transformed into a broader struggle between Capetian France and Imperial-supported Flemish independence, ultimately ensuring Flanders remained free of direct French rule for decades to come.

Consolidation of Thierry of Alsace’s Rule and the Flemish Conflict with Liège and Namur (1128 CE)

Following the death of William Clito in July 1128, Thierry of Alsace solidified his claim to Flanders, establishing his government in Ghent. Despite his Imperial-backed victory, Flanders remained unstable, with ongoing conflicts in Liège and Namur.

Godfrey of Leuven’s War Against Liège and Namur

• Godfrey I, Duke of Lower Lorraine, continued his military campaigns against the Prince-Bishopric of Liège and the County of Namur.
• As a key ally of the Capetians, Godfrey had previously supported William Clito’s claim to Flanders and remained opposed to Thierry’s rule.
• His war in the Meuse valley, which had begun before Clito’s death, continued as an independent regional conflict, shaping the balance of power in Lotharingia and northern France.

Thierry of Alsace Secures Power in Flanders

• Thierry established his rule in Ghent, one of the most economically and politically important cities in Flanders.
• He was recognized as Count of Flanders by the major Flemish cities, including Bruges, Lille, and Saint-Omer, confirming his legitimacy.

Anglo-Flemish Relations: Henry I’s Support for Thierry

• King Henry I of England, having previously supported William Clito, now shifted his allegiance to Thierry.
• Henry ordered his Flemish vassals in England to swear fealty to Thierry, reinforcing his political legitimacy and military backing.
• This Anglo-Flemish alliance secured English influence in Flanders, an economically vital trade partner.

Impact and Consequences

• Thierry’s recognition across Flanders marked the end of the immediate succession crisis following Charles the Good’s assassination.
• The continued fighting in Liège and Namur meant that Imperial-backed and Capetian-backed factions remained at odds, fueling ongoing regional instability.
• Henry I’s endorsement further strengthened Anglo-Flemish ties, ensuring that England retained influence over the Flemish trade economy.

Though Thierry had successfully secured his rule, Flanders remained entangled in the broader power struggles of France, the Empire, and England, setting the stage for future political realignments.