I would like to know which state actor are the USA protecting Europe from? Before anyone says Russia, I would like to point out that Russia is a country which is dying out pretty fast, has increasing problems with its muslim population, has China knocking on resource-rich Siberia, has a demoralized and ever-deteriorating military and has a leader who is not an idiot with suicidal tendencies. If it weren't for general population that wants its nation pictured as a superpower (yeah, just like in the USA), Russia would already admit that Europe is going to be its partner, not rival (if some conditions, like Central Asia being Russian playground, are met).
If there wasn't a bloated military-might benchmark in the form of the US Army, noone could seriously say that Europe is undermilitarized. Of course, our military is insufficient for stuff like encircling China, protecting Taiwan, being a substitute for Japanese army and such but then again, there's no reason for doing that in the first place. The world would not crumble if the USA focused on the essentials, i.e. economic and self-defense interests (and in the strict sense, not some all-encompasing one). Being everywhere overseeing everything is evidently not working and it costs too much money - and this problem will not fade away with time, it will grow with time passed. The world needs America that balances its current account deficit and gets into good economic shape, not America that decides which dictator may stay in power and which not.