How's This For A Premise?

1999: A World of Difference

On August 12, 1992, England's tiny nuclear arsenal fell on Ireland, South Africa, and finally on China. Instantly the planet went up in flames. In the first half of what was to be called the War of '92, half the Eath's population perished.

The United States was reduced to a vast underpeopled land--and, to make matters worse, Texas had seceded and taken her precious oil reserves.

But Israel, virtually untouched in a world ravaged by war, was painfully overpopulated. So Sol Ingelstein and Myra Kalen had come to America looking for a place to settle. As mercenaries on the side of the union in its war with Texas, the Israelis had been promised land in exchange for their services.

Leading their bedraggled troops into the heartland of Texas, Sol and Myra head up operation King. Mission: Resuce the President of the United States!

From The Texas-Israeli War: 1999 by Jake Saunders and Howard Waldrop (Del Rey, 1974). And yes, it's about as bad as it sounds.