In the Victorian era, America had been in the cultural orbit of Britain.
In the Modern era, America became much more influenced by continental Europe and vice versa. From the United States, jazz, rock, rap, eugenics, the American bathroom, Hollywood movies, Fordism and Nordicism were exported to Western Europe. From Western Europe, anarchism, communism, socialism and fascism, Modernism, Freudianism, the Boasian school of cultural anthropology, the Frankfurt School, the Austrian school of economics, existentialism and postmodernism were exported to the United States. Most importantly, a bunch of European scientists emigrated to the United States and built the atomic bomb. The cultural flow has gone on continuously across the American Empire since World War II.
The following excerpt comes from Robert M. Crunden’s book A Brief History of American Culture:
“The generation that matured creatively between the end of World War I and the beginning of World War II made the final transitions necessary for America to be a genuinely cosmopolitan culture. Earlier Americans had had to go abroad to meet their peers and be creative in a nurturing environment; they needed foreign academic training to complete a professional preparation that met the highest standards. A few became permanent expatriates, returning rarely if at all to the United States. Even where adequate, European-quality training was available, as at some of the graduate departments of the John Hopkins or at Harvard, the infrastructure of American culture was not truly able to absorb most of the products. The taste of the public was not sophisticated, review media were weak; too few colleges, museums, and concert halls were open to anything innovative.
By the 1920s and 1930s, this situation was fast ending. On the one hand, European scholars began their migrations in the face of postwar impoverishment, redrawn national borders, and political upheaval. Few countries could absorb many émigrés at any productive level even in times of peace, and with the imposition of dictatorships in Central Europe during the 1930s, more and more scholars and artists sought security in America.”
I’m not sure where to attribute liberal democracy and capitalism.
Both existed in Western Europe before World War I and World War II. The defeated Axis powers were forced to embrace liberal democracy and to join the Western Bloc in the Cold War. The important thing is that America’s puritanical culture was a casualty of this cultural exchange.
Note: This list doesn’t include all the European culinary contributions from the immigrants who came over in the Great Wave.