Moloch was the oldest and most powerful of the Elder Gods, who according to legend was born in "the fires of creation", and was the god of chaos.
He had agents to do his work for him and they possessed several real life humans including Albert and Peggy Marsden, who were instructed to destroy the Earth. But these two were trapped inside a pocket dimension created by the Seventh Doctor. The dimensional prison took the form of a ten-day time loop and only existed as long as the Elder Gods were trapped within it, preventing Moloch from freeing them. The Doctor meant them to understand what it was to live and die as mortal humans, and promised to release them once they could do this; however, they were left trapped for several hundred years.
In the alternative timeline created by Moloch in the hope of destroying Earth, the militant hardliner Vladimir Kryuchkov became the General Secretary of the Communist Party of the Soviet Union following the death of Konstantin Chernenko in 1985 rather than the considerably more moderate Mikhail Gorbachev. A nuclear war which came to be known as World War III broke out between the United States and its allies including the United Kingdom on the one hand and the Soviet Union on the other hand on 9 November 1989. Given that nuclear weapons were used by both sides, hundreds of millions of people were killed in the conflict. This timeline was ultimately negated by the Seventh Doctor. (AUDIO: Protect and Survive)