Axis military efforts in the Balkans, compared with the rest of Europe, had not gone well. Italy had invaded Greece in October 1940 but was pushed back into Albania. Germany then put pressure on Yugoslavia to join the Axis, as Romania, Hungary and Bulgaria had done earlier. Prince Regent Paul of Yugoslavia relented and signed the pact on March 25, 1941.
However, nationalist forces violently opposed the idea and carried out a coup. That led Hitler to view Yugoslavia as a hostile state; he decided to bomb Belgrade in retribution. On April 6, 1941, the Axis Powers (Hungary, Italy, led by Germany) invaded Yugoslavia, killing thousands of civilians and soldiers and capturing another quarter million; Yugoslav forces were unable to stop the bombardments or the advance of ground forces. The invasion ended with the unconditional surrender of the Royal Yugoslav Army on April 17.