My answer to How would the nations respond if the US brought home all its military, and said we're not doing this a…
Answer by Ken Larson:
Nations in which we have a presence would be notified in advance or our leaving, since the U.S. is a member of NATO and has other international agreements that it upholds.
There would then be geopolitical pressures applied and negotiated resulting in the U.S. keeping its forces in countries that must have them to strategically prevent war with Russia and North Korea.
In the Middle East, the U.S. would depart unilaterally and much like the Vietnam experience, that part of the world would move on without our influence for better or worse. Why? Because we will have finally learned the cause and effect impact of the costly incursions there over the last 15 years.