On April 6th, the German 2nd and 12th Armies, Italian 2nd and 9th Armies, and the Hungarian 4th, 5th and Mobile Corps invaded Yugoslavia from Italy, Germany, Romania, Bulgaria and Albania. Few of the Royal Yugoslav Army's 30 divisions actively resisted, and after 11 days the Yugoslav High Command surrendered. In Croatia, a puppet state was installed. Axis forces quickly occupied the principal towns and patrolled the main road and rail links, but in the villages, countryside and mountains, a vicious and complex guerrilla war was brewing. This title takes a close look at the German, Italian, Croatian, Serbian, Montenegrin, Bulgarian, Macedonian, and Slovenian units that fought for the Axis powers in Yugoslavia during World War II.