The Second World War was largely the result of the failures of the Treaty of Versailles of World War I. When the Allied powers of Great Britain, France, and the United States finalized the Treaty of Versailles in 1919, Germany was blamed for the war and faced many steep punishments. From 1919 to 1939, Germany experienced an economic recession that fostered resentment toward the Allied nations and allowed for fascist ideology to develop in Germany. World War II officially began when Germany, under the leadership of Adolf Hitler, invaded Poland on September 1, 1939. As a result of the Treaty of Versailles, Germany and the Soviet Union lost territory that became Poland. In August of 1939, Germany and the Soviet Union signed the Non-Aggression Pact and the two countries agreed they would not take military action against each other for ten years, planned for the joint invasion of Poland, and a secret agreement to divide Eastern Europe. Two days after the invasion of Poland, Great Britain and France declared war on Germany. While the invasion of Poland has been noted as the start of World War II.