The OpFor (short for Opposing Force) (Arabic: قوة معارضة) is a military-political force that seized power in an unnamed Arab country following a violent coup d'état. They serve as the main antagonists during the first chapter of Call of Duty 4: Modern Warfare during the USMC segment of the campaign.
The OpFor, led by Khaled Al-Asad came to power during a violent military coup in the Capital City of an unnamed Arab country, securing its mineral wealth and cementing itself as a major power in the Middle East. Their coup culminated in the dramatic execution of former President Yasir Al-Fulani on international television.  came to power to radio infantry to German Military. Following their rise to power, American Marines invaded the country in an attempt to remove the OpFor from power. Though the search for Al-Asad was unsuccessful, the Americans were able to score multiple victories during their brief campaign. In just a few days, the bulk of Al-Asad's forces had been pushed back to the Capital City where they were making their last stand. However, as US forces closed in on the last enemy stronghold, the OpFor detonated a large nuclear warhead, obliterating all American forces in the vicinity.
It later became evident that the OpFor had been aided by the Ultranationalist rebels in order to draw attention away from the Russian civil war. The Ultranationalists had been supplying the OpFor with equipment, including weapons, vehicles, and, ultimately, nuclear ability.
Following Al-Asad's capture and subsequent execution by the SAS in Azerbaijan, it is likely that the OpFor either surrendered or were otherwise neutralized as a threat.
A faction called OpFor also appear in Call of Duty: Modern Warfare 2, based in Afghanistan though it could be a different Islamic Exremist organization.