The Kingdom of Bulgaria, under Tsar Boris III, aligned itself with Adolf Hitler's Nazi Germany, and as a result regained Southern Dobruja in the Treaty of Craiova of September 1940, and occupied Western Thrace, and much of Macedonia after the Germans invaded Yugoslavia and Greece in April 1941. In the Bulgarian Army, there were four or five field armies, including the First Army, and some 30 divisions. On 22 June 1941, the First Army included the 1st Division; the 7th Division (); two border guard regiments, a machine-gun battalion, other artillery units, engineers, and other supporting units.