One year after Boris became tsar, Aleksandur Stamboliyski of the Agrarian Union was elected prime minister. Though popular with the large peasant class, he earned the animosity of the middle class and military, which toppled his government in 1923. In 1925, Greece declared war. Despite the intervention of the League of Nations, the turmoil continued until 1934, when Boris helped the military establish a dictatorship. The following year, he assumed control of the country, ruling as absolute monarch.
In the early days of World War II, popular sentiment swayed toward Germany, which forced Romania to cede Dobruja to Bulgaria. In 1941, Boris officially allied himself with the Axis powers and participated in Germany's war against Greece and Yugoslavia. In his defense, however, it can be argued that he was simply trying to regain the territory lost in the Treaty of Neuilly. On the other hand, he refused to cooperate with Adolf Hitler's anti-Semitic campaign and refused to surrender the country's Jewish population to the Nazis during the Holocaust. Most threatening to Hitler, however, was the tsar's refusal to declare war on the Soviet Union, even in the most critical moment, when the war was turning against Germany.
In 1943, Hitler summoned Tsar Boris to a stormy meeting in Berlin. While Boris agreed to declare war on the distant United Kingdom and United States, he refused to get himself involved in a war against the Soviets. Shortly after Boris returned to Sofia, he died of apparent heart failure, though many believe he was poisoned by Hitler in an attempt to put a more fervently pro-Nazi government in place. Boris was succeeded by his six-year-old son Simeon II.