 Complete the following phrase:  Bulgaria succeeded in negotiating a recovery of Southern Dobruja, part of Romania since 1913, in the Axis-sponsored Treaty of Craiova on 7 September 1940, which reinforced Bulgarian hopes for solving territorial problems without direct involvement in the war. However, Bulgaria was forced to join the Axis powers in 1941, when German troops that were preparing to invade Greece from Romania reached the Bulgarian borders and demanded permission to pass through Bulgarian territory. Threatened by direct military confrontation, Tsar Boris III had no choice but to join the fascist bloc, which was made official on 1 March 1941. There was little popular opposition, since the Soviet Union was in a 