I'd argue that as far back as the 30's European manufacturers were making cars every bit as good as those made in America.
That said, they were and are made to a different design ethos - American cars have never been designed for balanced performance like German cars have, they instead have been designed for comfort and trouble-free operation (meaning next to no maintenance). America long made the only car in the world that could go 100,000 miles with nothing but fluid changes, and other wear items. No European car can really do that, all of the German makes have a pretty aggressive preventative maintenance schedule.
Japan to an extent does build cars to the american ethos - they build to the American ethos, but localized to the Japanese market to a greater or lesser extent -but then again they were taught car building by the Americans after WWII - which is I think why Japanese cars have been so successful in the American market.
