Why Britain and France Did Not Declare War on the Soviet Union in 1939

During the tumultuous period of World War II, the decision by Britain and France not to declare war on the Soviet Union following its invasion of Poland in September 1939 has often been a subject of historical debate. This decision was multifaceted, rooted in strategic, political, and military considerations. Below, we delve into the reasons behind this decision and its implications.

Focus on Germany: The Primary Threat

The primary motivation for Britain and France in declaring war on Nazi Germany, rather than the Soviet Union, was the belief that Germany posed the greatest and most immediate threat to European stability. This is reminiscent of the British approach during World War I, where their main goal was to contain Germany rather than any other power. Germany’s invasion of Poland on September 1, 1939, significantly altered the regional balance of power and signaled the start of a conflict that both nations were determined to prevent from spreading into a wider war.

Molotov-Ribbentrop Pact and Non-Aggression

The Molotov-Ribbentrop Pact, signed in August 1939, was a mutual non-aggression agreement between Nazi Germany and the Soviet Union, which included a secret protocol dividing Eastern Europe into spheres of influence. This agreement, while concerning, allowed both powers to invade Poland without immediate conflict. However, this pact did not go unnoticed. Churchill, a staunch opponent of the Soviets, recognized that this alliance would not last and that Germany would eventually violate the non-aggression agreement. However, Britain and France chose not to act on this potential future threat, prioritizing the immediate danger posed by Germany.

Strategic Calculations and Military Capabilities

Britain and France were also aware that declaring war on the Soviet Union could lead to a broader conflict involving other nations, complicating their military strategies. At that time, they were only beginning to mobilize their military forces against Germany and were not prepared for a two-front war. Declaring war on the Soviet Union would have required significant military investments and strategic shifts that were not feasible at the time. The strategic calculus involved in such decisions is complex and often prioritizes current and immediate threats over potential future ones.

Political Considerations and Tolerance

There was also a political consideration among some Western leaders that the Soviet Union could serve as a counterbalance to Nazi Germany. This hope led to a certain degree of tolerance toward Soviet actions in Eastern Europe, as long as they did not directly threaten Western interests. While the Soviet invasion of Poland on September 17, 1939, was undoubtedly a violation of the non-aggression pact, the Western powers believed that engaging the Soviet Union at that point could exacerbate the conflict and potentially end up with an even worse situation.

Subsequent Developments

As the conflict progressed, the invasion of Poland by the Soviet Union became more of a political and military strategy rather than an immediate cause for declaring war. Britain and France had already committed to their war effort against Germany, and the invasion was largely viewed through the lens of the larger conflict. The Soviet Union’s actions were seen as a result of its own interests rather than an immediate threat to Western Europe, further delaying any potential decision to declare war.

In summary, the decision by Britain and France to not declare war on the Soviet Union in 1939 was a complex and multifaceted choice, driven by strategic, military, and political considerations. While Churchill and others recognized the potential threat posed by the Soviet Union, the immediate and pressing threat of Nazi Germany remained the primary focus of their strategic decisions during World War II.