Summary
Highlights
After Hitler broke the Munich Agreement by occupying Czechoslovakia in March 1939, Britain began to rearm, recognizing that confrontation was unavoidable. Chamberlain admitted appeasement failed and warned Hitler that Britain valued freedom more than peace. Britain, initially unprepared for war due to post-WWI defense cuts, abandoned the '10-year rule' in 1932. The Defense Requirements Subcommittee (DRC) evolved its recommendations from fearing Japan in 1934 to anticipating war with Germany, Italy, and Japan by 1936. Britain prioritized building up the Royal Air Force and Royal Navy, modernizing with new aircraft and ships, but the army's modernization lagged. Despite increased military production, Britain remained ill-prepared for a continental war on the eve of conflict, with significantly fewer men and resources than Germany.
With Czechoslovakia under German control, Poland became Hitler's next target. Chamberlain reversed his policy, guaranteeing British support to Poland via the Anglo-Polish Agreement, committing Britain to war despite lacking resources. Critics argued this gave Poland undue influence over Britain's war decisions. Chamberlain hoped to deter Hitler, but Hitler, believing aggression would not be opposed, demanded Danzig's return and access across the Polish Corridor. Emboldened by British support, Poland refused concessions. Britain, France, and the USSR attempted to negotiate an alliance to defend Poland, but distrust between Poland and the USSR, and Chamberlain's dislike of communism, led to its failure.
With no Anglo-French alliance, Stalin sought to protect USSR's interests. On August 24, 1939, Germany and the USSR signed the Nazi-Soviet Pact (Molotov-Ribbentrop Pact), a non-aggression treaty with a secret protocol dividing Eastern Europe. Stalin signed due to failed alliance attempts with Western powers, distrust after Munich, threats from Japan, and a desire to delay a German attack for preparation. Hitler benefited by securing Soviet neutrality for his planned invasion of Poland, confident Britain and France would not intervene.
Convinced Britain and France would not act, Hitler staged a fake Polish attack as a pretext and invaded Poland on September 1, 1939. Poland requested British and French military support, who issued an ignored ultimatum to Germany. On September 3, 1939, Britain and France declared war on Germany, initiating their involvement in World War II. Britain enacted conscription for men aged 18 to 41. The USSR invaded eastern Poland on September 17, as per the Nazi-Soviet Pact.
The causes of World War II were a combination of long-term and short-term factors: the harsh terms of the Treaty of Versailles, the failure of the League of Nations, the global economic crisis and rise of fascist dictators, fear of communism hindering a united front, appeasement emboldening Hitler, the Nazi-Soviet Pact, and Hitler's invasions of Czechoslovakia and Poland. Historians debate Hitler's motives, with some arguing he always intended a major war for conquest, citing Mein Kampf as evidence, while others view him as an opportunist who did not plan a major war, noting his caution and expectation that Britain and France would not intervene in Poland.