Decadence is a little too pat, for my mind. Europe scared itself with too much war, but also we put our boot on its neck and have occupied it for 60 years. Also they lost their colonies. They are scared of their own shadow, and we make it easy by protecting them. We need to withdraw our troops and make them stand on their own feet. The good news is that we have them actually fighting in the Middle East, though it took years for some to catch on that Afghanistan wasn't a tea party for peacekeepers in running togs.
I believe Europe has had it too easy too long.
They no longer had to defend themselves on any front. No cost living became a right.
Instead they began to believe that the peace they lived under was of their own making instead of through an umbrella of arms provided by the United States.