USA has troops in European countries (and elsewhere) not to protect them, but to have (1) political, military, intelligence and economic influence there, (2) to

USA has troops in European countries (and elsewhere) not to protect them, but to have (1) political, military, intelligence and economic influence there, (2) to use those countries as a launchpad to threaten (and eventually easier attack) countries who still haven't submitted to its power and which are in the vicinity of the countries harbouring the US troops, (3) to make it seem like its power is much greater by having "allies" (but, in reality, "vassals", as Zbigniew Brzezinski has called them in his book The Grand Chessboard). Or, as NATO’s first Secretary General, Lord Ismay, has put it: NATO exists to “keep the Soviet Union out, the Americans in, and the Germans down.” https://www.nato.int/cps/en/natohq/declassified_137930.htm https://www.nato.int/cps/en/natohq/declassified_137930.htm