The Hot War is an alternate history trilogy by Harry Turtledove. The first volume, Bombs Away, was released in July 2015. The second volume, Fallout, was released in July 2016. The concluding volume, Armistice, was released in July 2017. The series posits the Korean War spiraling into World War III in 1951, with the United States and the Soviet Union trading atomic bombs.
As is typical with Turtledove's multi-volume works, The Hot War embraces a number of POV characters, and rotates through them to tell the overall story.
See:Bombs Away for more details
The point of divergence is November 1950, when Chinese troops intervene in the Korean War, and do a much more thorough job of destroying various American forces between the Chosin Reservoir and Hungnam. (In OTL, the U.S. forces were defeated, but were able to successfully evacuate from Hungnam and inflict heavy casualties on the Chinese.) This prompts President Harry Truman to allow General Douglas MacArthur to use atomic weapons in Manchuria in January 1951, which prompts the Soviet to attack in Europe in retaliation. They drop atom bombs of their own in England, France, and West Germany, forcing the United States to join a hot war to defend its NATO allies. A ground war breaks out in Europe in February, 1951. For the remainder of the novel, the USSR and its allies drive relentlessly west, and several cities fall to atomic bombs. The novel closes in June, 1951, with the Soviets still driving west throughout Germany, Austria, and Italy.
See:Fallout for more details
The second novel picks up in mid June, 1951, in the aftermath of the atomic bombing of Paris, and ends in May 1952. The Soviet Union and its allies advance through West Germany in spite of heavy resistance from NATO forces. Desperate, the U.S. bombs the entirety of the Soviet front lines, finally breaking the advance. Both powers start suffering internal problems, as the Soviet Union's puppets start rebelling, while President Truman faces increasingly harsh criticism in the U.S.
In a desperate move, the USSR is able to attack the U.S. east coast, destroying Washington, DC, among other key cities. While Truman survives, most of the U.S. government does not. In the meantime, the Soviets continue their retreat, and are forced to contend with an uprising in Poland. The novel ends in May, 1952.