Britain and France Declare War

Honoring their guarantee of Poland’s borders, Great Britain and France declared war on Germany on September 3, 1939. Two days earlier, Germany had invaded Poland.

Despite the declaration of war, there was initially only limited engagement between the German and British militaries. This period is consequently known as the “Phoney War.” During this time, Germany was busy fighting in Poland. The British quickly established a naval blockade against Germany and then concentrated on mobilizing for war. On September 7, French troops invaded neighboring German territory in the Saarland, but the operation foundered, and within days French forces withdrew. The Phoney War ended in May 1940, when Germany invaded Belgium, France, and the Netherlands.