Ballroom of the Skies
John D. MacDonald
Nelson Doubleday 1979 (1951),
Practically a short story. Unfortunately, near the end they give an actual date: 1979. Oops.
WWIII happened in the early 1970s, leaving the US as a second-rate power allied to Pak-India. PI is opposed by a coalition including Irania and North China and WW IV is looming on the horizon. One man, Darwin Branson, has been working to prevent war but on the eve of a critical meeting he is killed and reprogrammed [or replaced by a simulacrum] by a mysterious couple. The new Branson is openly arrogant and cynical, and war is not to be averted.