How was Mao Zedong's ideology different from Marxist ideology?

Although Chairman Mao based his rule upon communism, which was derived from Karl Marx as interpretted by Lenin and Stalin (and then subjected to additional interpretation by Mao himself), Mao was a very ruthless man who showed no actual concern for the welfare of the people he ruled, contrary to the very idealistic philosophy of Marx. To give just one example of this, during a terrible famine in which millions of Chinese died of starvation, Mao continued to export food from China, because he needed the money to help finance his nuclear weapons program. Marx would have been deeply horrified.