On 1 March 1941, Bulgaria signed the Tripartite Pact and Tsar Boris III officially joined the Axis bloc. After a short period of inaction, the army launched an operation against Yugoslavia and Greece. The goal of reaching the shores of the Aegean Sea and completely occupying the region of Macedonia was successful. Even though Bulgaria did not send any troops to support the German invasion of the Soviet Union, its navy was involved in a number of skirmishes with the Soviet Black Sea Fleet, which attacked Bulgarian shipping. Besides this, Bulgarian armed forces garrisoned in the Balkans battled various resistance groups. The Bulgarian government declared a token war on the United Kingdom and the United States near the end of 1941, an act that resulted in the bombing of Sofia and other Bulgarian cities by Allied aircraft.