Americans went to Europe for grad school and/or postdoctoral research in science (especially in chemistry and physics) before WWII, though. We saw ourselves as second rate. People like Oppenheimer, Rabi, Pauling, and just about every other early-mid 20th century chemist or physicist did all or some of their training in Europe, Now, at least until recently, it's been Europe (and the rest of the world) flocking to our universities.