In response, Britain and France declared war on Germany and later, its ally Italy.

At the same time, the Soviet Union occupied eastern Poland, but remained officially neutral in the war under a secret pact with Germany.

During the next two years German forces were victorious, invading Denmark and Norway, the Low Countries (Belgium, the Netherlands, and Luxembourg) and France, Yugoslavia, and Greece.

The Soviet Union occupied the Baltic countries (Lithuania, Latvia, and Estonia) and eastern Romania, and attacked Finland.

Slovakia, Hungary, Romania, and Bulgaria allied with Germany.

In June 1941, Germany attacked the Soviet Union.

A second German offensive in 1942 brought German forces deeper into Soviet territory. That same year, German and Italian forces occupied the southern zone of France.

In 1942 and ‘43, Soviet forces counterattacked and began liberating territory from German domination. In the west, Allied forces landed in North Africa and invaded Italy.

In 1944, Allied forces landed in northern France, beginning the liberation of western Europe.

Meanwhile, from the east, Soviet forces continued their advance.

Following the German surrender in May 1945, the Allied victory in Europe was complete.