Merc: 2000

From the back of the book:

MERC: 2000 is a game of daring night raids on enemy camps. Audacious hostage rescues, and tense industrial sabotage missions in exotic foreign locales. It is an alternate world situation for use with Twilight: 2000, GDW’s roleplaying game of survival in a devastated world. In MERC: 2000, the world did not blow itself up. The old bi-polar superpower conflict is gone, replaced by a mulitpower competition. What armies remain are kept purely for internal security at reduced levels. When a war becomes necessary, a country (or company) will hire independent contractors "mercenaries" to conduct it.

It is an alternate world situation for use with Twilight: 2000. Using Twilight: 2000 rules as a base, MERC: 2000 enables players and referees to recreate modern close combat in a number of environments. MERC: 2000 includes a new chronology of the events of the decade between 1990 and 2000, plus new rules, equipment, vehicles, weapons, and career path (counterterrorist). It also contains five ready-to-play scenarios and suggestions for scenario creation and campaign organization. Everything is fully compatible with the Twilight: 2000 rules system, and characters can be used interchangeably.

2000AD, although related, is an alternate history that included nuclear war and is thus not a part of this setting.