The statement that most accurately describes the reason the Soviet Union invaded Afghanistan is: "The Soviet Union wanted a puppet leader there to fulfill its wishes."
The invasion, which occurred in December 1979, was largely motivated by the Soviet Union's desire to support the communist government of Afghanistan against insurgent groups and to establish a regime that would align more closely with Soviet interests in the region. The Soviets aimed to maintain influence in Afghanistan and prevent the spread of Western or anti-communist ideologies, particularly as the situation in the country was becoming increasingly unstable.