Mr. Mugabe is a British-educated communist, as we are told, the most highly educated of any African dictator. As a communist, one of his goals would be to destroy the national sovereignty of the US.
Perhaps his purpose in Zimbabwe (and his payoff to the Americans (Carter/Brezinski) and British who put him in charge) is to provoke the "international community" into declaring national sovereignty void in the "humanitarian interest." He might see it in his long term interest toward picking Western pockets clean, devolving American power, and clearly enjoys the continuing pleasures of limitless despotism. He probably regards his political opponents as deserving death and really doesn't care what happens to Zimbabwe in the process toward global communism.