Why are we spending so much to protect Europe?

Since 1941 when the US started to save Europe after their massive failure to contain Hitler when he was weak the US has spent enormous amounts of your money to keep Europe safe. During the Cold War the European countries that weren't under the thumb of Russia counted on the US to keep them free and spent their money to build welfare states.

Given that the Europeans, with the exception of England, were too lazy to protect themselves America was forced to protect them since if the Soviets took over all of Europe it would be bad for the US.

But now there is no reason for the US to defend Europe from anything. Europe as a whole as a GDP of $18.7 trillion which is very close to that of the US and far beyond the Russian GDP of $1.7 trillion.

It's clear that we benefit from NATO but we should be, as Obama would say, leading from behind with the US military only coming in to increase the odds in Europe's favor not as the primary force in any conflict.

Other countries have been robbing us blind through unfair trade deals the US agreed to when we were fighting the Soviets and rebuilding the world after WWII but they're also robbing us by counting on the US to defend them.