The Soviet Union enters the Second World War on September 17, 1939, with its invasion of Poland, in accordance with a secret protocol within the Molotov–Ribbentrop Pact with Nazi Germany.

The Soviet Union later invades Finland, and occupies and annexed the Baltic states, as well as parts of Romania.

On June 22, 1941, Germany invades the Soviet Union, opening the Eastern Front, the largest theater of the war.

Some five million Red Army troops will be captured eventually by the Nazis; the latter deliberately starve to death or otherwise killed three point three million Soviet POWs, and a vast number of civilians, as the "Hunger Plan" seeks to fulfill Generalplan Ost.

Although the Wehrmacht has considerable early success, their attack is halted in the Battle of Moscow.

Subsequently, the Germans are dealt major defeats first at the Battle of Stalingrad in the winter of 1942–1943, and then in the Battle of Kursk in the summer of 1943.

Another German failure is the Siege of Leningrad, in which the city is fully blockaded on land between 1941 and 1944 by German and Finnish forces, and suffers tarvation and more than a million deaths, but never surrenders.

Soviet forces steamroll through Eastern and Central Europe in 1944–1945 and capture Berlin in May 1945.

In August 1945, the Red Army invades Manchuria and ousts the Japanese from Northeast Asia, contributing to the Allied victory over Japan. 

Northeast Europe (1936–1947 CE): Geopolitical Crisis, War, Occupation, and Postwar Realignment

Between 1936 and 1947 CE, Northeast Europe underwent seismic changes marked by the increasing geopolitical tensions preceding World War II (1939–1945), severe wartime experiences, occupations, resistance movements, and complex postwar realignments. Finland, Estonia, Latvia, and Lithuania faced unprecedented challenges from aggressive German and Soviet expansionism, dramatically reshaping their national fates. Denmark, Sweden, and Norway navigated wartime neutrality, occupation, and resistance in varied ways. The immediate postwar years set the stage for regional geopolitical shifts and long-lasting consequences.

Prelude to War: Rising Tensions and Shifting Alliances (1936–1939)

In the late 1930s, Northeast Europe faced escalating geopolitical pressures as Nazi Germany under Adolf Hitler intensified expansionist policies. Simultaneously, the Soviet Union under Joseph Stalin increasingly asserted control over the Baltic region. Finland, Estonia, Latvia, and Lithuania confronted diplomatic and military threats from both major powers, leading to heightened defense preparations and strained diplomatic relations.

In August 1939, the Molotov–Ribbentrop Pact between Germany and the Soviet Union secretly divided Eastern Europe into spheres of influence. Estonia, Latvia, Lithuania, and Finland were assigned to the Soviet sphere, marking a devastating turning point.

Finland: The Winter War, Continuation War, and Resilience

In November 1939, the Soviet Union launched the Winter War (1939–1940) against Finland, demanding territorial concessions. Despite vastly outnumbered Finnish forces, under the leadership of Marshal Carl Gustaf Emil Mannerheim, Finland resisted fiercely, gaining international respect. Finland ultimately signed the Moscow Peace Treaty (1940), ceding territories including Karelia but preserving national sovereignty.

In 1941, aligned with Germany in the Continuation War (1941–1944), Finland sought to reclaim lost territories. The Finnish army advanced significantly, but by 1944, the Soviet counter-offensive compelled Finland to negotiate. In September 1944, Finland signed the Moscow Armistice, leading to territorial losses and reparations, yet retaining independence and democratic governance.

Baltic States: Occupation, Resistance, and Loss of Independence

Estonia, Latvia, and Lithuania faced a far more devastating fate. Under Soviet pressure following the Molotov–Ribbentrop Pact, all three countries were occupied in June 1940 and forcibly incorporated into the Soviet Union through rigged elections. Brutal repression followed, including mass deportations, executions, and imprisonment of tens of thousands of citizens.

In June 1941, Nazi Germany invaded the Soviet Union (Operation Barbarossa), quickly occupying the Baltic region. Initially welcomed as liberators by many, German forces soon imposed a brutal regime marked by persecution and extermination, especially of the Baltic Jewish communities, tragically destroying centuries-old vibrant cultures.

National resistance movements emerged, such as the Forest Brothers, guerrilla fighters opposing both Soviet and Nazi occupations. The Baltic states suffered immense human losses, economic devastation, and profound social trauma.

By 1944–1945, Soviet forces reoccupied Estonia, Latvia, and Lithuania, reasserting control. All three nations lost their independence for nearly five decades, forced into the Soviet Union as republics.

Denmark: Occupation and Resistance

In April 1940, Germany occupied Denmark with minimal resistance. Initially permitted some autonomy, Danish society and economy soon faced severe restrictions. However, Danish resistance strengthened significantly, exemplified by the rescue of Danish Jews in 1943, secretly ferrying thousands to safety in Sweden.

The Danish resistance movements sabotaged German military operations, supported by secretive intelligence collaboration with Allied forces. Liberation came in May 1945, restoring Danish democracy and sovereignty.

Norway: Occupation, Resistance, and Liberation

Norway’s experience was marked by immediate resistance to Germany’s April 1940 invasion. Despite brave Norwegian military defense, notably at battles such as Narvik, Norway fell under Nazi occupation, governed harshly under the puppet regime led by Vidkun Quisling, whose name became synonymous with treachery.

Strong resistance groups formed, engaging in sabotage, underground intelligence activities, and collaboration with Allied forces. The Norwegian exile government in London, led by King Haakon VII, symbolized national continuity and resistance. Liberation by Allied forces in May 1945 reinstated democratic governance and national sovereignty, profoundly influencing postwar identity and foreign policy.

Sweden: Armed Neutrality and Humanitarian Aid

Sweden remained neutral throughout the war, carefully balancing diplomatic relations. However, Swedish neutrality faced challenges, including occasional concessions to Germany such as permitting transit of German troops and supplies.

Nevertheless, Sweden significantly supported humanitarian actions, sheltering refugees from across Nazi-occupied Europe. The dramatic rescue of Denmark’s Jews in 1943 exemplified Swedish humanitarian commitments. Sweden’s postwar stability positioned it as a strong advocate of international peace and human rights.

Wartime Economies and Social Transformations

Throughout wartime, economies across Northeast Europe underwent severe disruption. Finland and Baltic states experienced massive destruction, infrastructure damage, and severe population losses. Denmark and Norway faced economic exploitation under Nazi occupation, despite pockets of resilience fostered by resistance networks.

Conversely, Sweden’s neutrality protected its economy from devastation, enabling postwar economic growth. In all countries, wartime hardships reshaped societies profoundly, catalyzing shifts toward greater social solidarity and subsequent postwar welfare state expansions.

Postwar Realignments and Soviet Dominance (1945–1947)

Postwar settlement dramatically reshaped Northeast Europe. The Yalta and Potsdam conferences (1945) confirmed Soviet control over Estonia, Latvia, Lithuania, and territorial concessions from Finland. While Finland retained sovereignty, it endured heavy war reparations and diplomatic isolation under strict Soviet oversight, exemplified by the 1948 Treaty of Friendship, Cooperation, and Mutual Assistance.

Estonia, Latvia, and Lithuania faced intensified Soviet repression, mass deportations, collectivization, and forced industrialization. These states disappeared as independent entities, suppressed behind the Iron Curtain.

Denmark and Norway quickly recovered democracy, engaging actively in postwar European reconstruction. Sweden, benefiting from wartime neutrality, positioned itself as a leader in humanitarian efforts, economic cooperation, and global peace initiatives, notably supporting the fledgling United Nations (founded 1945).

Cultural Resilience and Postwar Reconstruction

Despite devastation, Northeast European nations preserved vibrant cultures through resilience. Finland reaffirmed national identity through educational initiatives, music, literature, and democratic institutions. In the occupied Baltic states, cultural survival became an act of resistance, with underground education, secret publications, and cultural preservation resisting forced Sovietization.

Scandinavian nations embraced postwar reconstruction enthusiastically, promoting democracy, welfare reforms, and extensive educational initiatives to repair war-torn societies and foster peaceful development.

Legacy of the Era

The period 1936–1947 CE fundamentally altered Northeast Europe's historical trajectory, characterized by brutal occupations, heroic resistance, national traumas, and subsequent division between East and West. Finland’s courageous defense preserved its independence, though at great cost. Estonia, Latvia, and Lithuania faced tragic fates, losing independence under Soviet control until the late twentieth century. Denmark, Norway, and Sweden emerged stronger in democracy, social cohesion, and international cooperation.

These transformative years profoundly impacted national identities, diplomatic alignments, and regional geopolitical structures, setting the stage for the Cold War's division of Europe and profoundly shaping Northeast Europe's political, social, and cultural evolution throughout the remainder of the twentieth century.