On 20 November 1940, under pressure from Germany, Pál Teleki affiliated Hungary with the Tripartite Pact. In December 1940, he also signed an ephemeral "Treaty of Eternal Friendship" with Yugoslavia. A few months later, after a Yugoslavian coup threatened the success of the planned German invasion of the Soviet Union (Operation Barbarossa), Hitler asked the Hungarians to support his invasion of Yugoslavia. He promised to return some former Hungarian territories lost after World War I in exchange for cooperation. Unable to prevent Hungary's participation in the war alongside Germany, Teleki committed suicide. The right-wing radical László Bárdossy succeeded him as prime minister. Following the Invasion of Yugoslavia and the proclamation of the Independent State of Croatia, Hungary annexed Bácska, the remainder of Baranya, Muravidék and Muraköz.