Peacekeepers — Ben Bova

PEACEKEEPERS
Created by the Athens Peace Conference in the wake of nuclear war in the Middle East, assigned control of every nation's orbiting nuclear hardware, the International Peacekeeping Force's brief is to prevent any military action across national borders, anywhere in the world. Period.

RENEGADES
The IPF is up to dealing with the normal run of chicanery. But when super-terrorist Jamal Shamar makes off with the world's last half-dozen nuclear warheads, a new force is needed:

MERCENARIES
...an elite, clandestine force available to anyone, anywhere, as long as the cause is world peace.