"King's government" in 1935, Bulgaria entered an era of prosperity and astounding growth, which deservedly qualifies it as the Golden Age of the Third Bulgarian Kingdom. It lasted nearly five years, governed by prime minister Georgi Kyoseivanov. Kyoseivanov's Premiership oversaw the trials of the instigators of the 1934 military coup and also concluded pacts with Yugoslavia and Greece as Nazi Germany undertook a policy of economic isolation of the Balkans. His government also oversaw a policy of rearmament after a treaty concluded with Ioannis Metaxas overturned the military clauses of the Treaty of Neuilly-sur-Seine and the Treaty of Lausanne. Although the signing of the Salonika Agreement of 1938 restored good relations with Yugoslavia and Greece, the territorial issue continued to simmer. World War II The government of the Kingdom of Bulgaria under Prime Minister Georgi Kyoseivanov declared a position of neutrality upon the outbreak of World War II. Bulgaria was determined to observe it until the end of the war, but it hoped for bloodless territorial gains to recover the territories lost in the Second Balkan War and World War I, as well as gain other lands with a significant Bulgarian population occupied by neighboring countries. However, it was clear that the central geopolitical position of Bulgaria in the Balkans would inevitably lead to strong external pressure from both World War II factions. On 15 February 1940, following the resignation of Georgi Kyoseivanov, a pro-German Bogdan Filov was appointed Prime Minister of the Kingdom of Bulgaria. On 7 September 1940 Bulgaria succeeded in negotiating the recovery of Southern Dobruja in the Axis-sponsored Treaty of Craiova. Bulgaria also had a non-aggression pact with Turkey. On 1 March 1941 Bulgaria formally signed the Tripartite Pact, becoming an ally of Nazi Germany, the Empire of Japan, and the Kingdom of Italy. German troops entered the country in preparation for the German invasions of the Kingdom of Greece and the Kingdom of Yugoslavia. When Yugoslavia and Greece were defeated, Bulgaria was allowed to occupy all of Greek Thrace and most of Macedonia. Bulgaria declared war on Britain and the United States but resisted German pressure to declare war on the Soviet Union, fearful of pro-Russian sentiment in the country. In August 1943 Tsar Boris died suddenly after returning from Germany from heart failure, but also rumoured to be poisoned. He was later succeeded by his six-year-old son Simeon II. Power was held by a