The Hungarians sent troops to help Hitler in the invasion of Russia in 41
Big Big Mistake.
In July 1941, the Kingdom of Hungary, a member of Tripartite Pact, took part in Operation Barbarossa, in alliance with Nazi Germany. Hungarian forces fought shoulder to shoulder with the Wehrmacht, and advanced through Soviet Ukraine, deep into Russia, all the way to Stalingrad. By 1943–1944, the tide of the war had turned. The Red Army regained the pre-war Soviet territory, and advanced westward from its borders to defeat Germany and its allies.
It was in the context of these events that the Budapest Offensive took place in September 1944. As the Hungarian army ignored the armistice with the USSR (signed by the government of Miklós Horthy on October 15, 1944), the Soviets fought against the Hungarian troops and their German allies, capturing the capital on February 13, 1945, and continuing military operations until April 4, 1945 when the last German forces and the part of Hungarian troops that chose to stay loyal to Germans, despite another armistice (signed by the government of Ferenc Szálasi), were routed.