After WW2 1945 Europe was so bombed out half rubble.
Russia used that situation formed "Eastern Bloc" The Former USSR
USA & Europe got together 50 more years fought a "Cold War" with Ruissia the USSR
Europe even after rebuilding and establing their economies never invested in millitary infrastructure just assumed AMERICA got their backs.
Nowadays even former European superpowers got a fraction their millitaries 50 some years ago.
But they let us build bases and support them but never really grew their own armies nor equipted them.
Russia rolling into Ukraine was a Big Shock.
Donald Trump just wants NATO members pay afew bucks more & expand their infrastucture.
Under NATO they aint hadda worry about their own defense Uncle Sam has guarateed that.
We still shall probably but just asking European Union stay "Loyal" & contribute their "Fair Share" in Defense $pending