Defenses against potential enemies do not necessarily have to be set up in 700 places around the globe. Our forefathers were not blind to threats from foreign entities. While they may not have envisioned modern warfare, they certainly did not envision build a worldwide empire as if the whole world was waiting with open arms for Western ideals.
It has little to do with having a “world wide empire” but more to do with having boots on the ground, making friends, being there in person. Showing unity when requested as we are in many countries (at their request) - to keep others at bay.
If we fail to do that, then they will succumb to influences that are totally against our interests.