In the spring of 1941, Germany began to make preparations for invading Greece and Yugoslavia for consolidating its position in the Balkans.

On March 1, 1941, German Ambassador to the USSR F. von der Schulenburg informed Soviet People’s Commissar of Foreign Affairs V. Molotov about the entry of German troops into the Balkans. In the name of the Soviet government, Molotov declared that Germany was infringing upon the security interests of the Soviet Union.

On March 25, 1941, Germany made Yugoslavia enter the Tripartite Pact. the same evening, protests broke out in Belgrade and other cities in the country. In the night of March 27–28, a group of patriotically minded officers formed a new government headed by General D. Simović. On March 27, Hitler ordered the invasion of Yugoslavia.

Having no illusions about Germany’s intentions, the new Yugoslav government tried to obtain the support of the Soviet Union. On April 5, 1941, the Treaty of Friendship and Non-­Aggression between the USSR and the Kingdom of Yugoslavia was signed in Moscow.

The following day, Germany attacked Yugoslavia, subjecting Belgrade to massive aerial bombardment (‘Operation Retribution’). the German invasion of Greece began at the same time.

In a lightning campaign, the Wehrmacht defeated the Yugoslav and Greek Armies and the British Expeditionary Force. the Balkans came under total German control.

In a letter of April 3, 1941, British Prime Minister W. Churchill told J. Stalin that Germany had postponed its invasion of the USSR due to the events in Yugoslavia.

Germany was unable to complete the deployment of its main forces in the East by May 15 – the date set by Operation Barbarossa. At a meeting of the Wehrmacht High Command on April 30, a new date was chosen for the invasion of the USSR: June 22, 1941.