For the early 1960s according to Daniel Ellsberg: "The total death toll as calculated by the Joint Chiefs, from a U.S. first strike aimed primarily at the Sovi

For the early 1960s according to Daniel Ellsberg: "The total death toll as calculated by the Joint Chiefs, from a U.S. first strike aimed primarily at the Soviet Union and China, would be roughly 600 million dead. A hundred Holocausts" 600 million was known at the time to be an underestimate and then add in what the Soviets would have done then over a billion is probably realistic. World population at the time was about 3 billion. Edit: Worth noting that this US strike would have killed about 100 million in Western Europe.