Fortress America depicts an alternate near-future in which all of the world attacks and invades the continental United States. From the west arrives hordes of Asian foes; from the south arrives a union of South American countries through Mexico, and from the east lands come legions of Soviets who have taken over all of Europe. America besieged has to rely on the remaining ground and air forces left in the country along with partisan uprisings to defend mom's apple pie.
Up to four players can play Fortress America, one player being the U.S. and up to three others controlling the invading units from a particular direction. Being a near future scenario, the units in the game include conventional infantry, APCs, hovertanks, helicopters, bombers, US partisan units, and special "Star Wars" laser relay systems that fire from space.