The Nazi-Soviet Pact signed in August 1939 was a turning point that made Hitler's plans for invasion more achievable. It ensured Germany would avoid a two-front war by allying with the Soviet Union and allowing them to divide up Poland between them. This removed a major strategic concern for Hitler and made it difficult for him to change course once the pact was signed, opening the door for Germany to invade Poland on September 1st and precipitating Britain and France's declaration of war against Germany.