“The Austro-Hungarian Empire was more diverse, with German and Hungarian minority nobilities ruling large populations of Czechs, Slovaks, Ruthenians, Poles, Ukrainians, Romanians, Serbs, Croats, Slovenes, Bosnians, and Italians”
America has fAmilies representing all of them and dozens never included in the Austro-Hungarian Empire as well. From Africa alone America has folks from Nigeria, Egypt, Ghana, Ethiopia, South Africa, Kenya, Liberia, Somalia, Morocco, Cape Verde, Sierra Leone and Sudan (and a few others). America has citizens and immigrants from every nation in Asia, Every nation in the Middle East, every nation in Latin America and every nation in Europe, including both Russia and Ukraine.
The Austro-Hungarian Empire may have been ethnically rich from a European point of view but it was no America.
In the US, the European ethnic groups have intermarried and assimilated and largely lost their ethnic identities. So their is a largely uniform white majority and Blacks (13%) and Hispanics (18%) as the major minority ethnic groups. Blacks have some solidarity, although recent immigrants from Africa or the West Indies are definitely different from ex-slave US blacks. Hispanics and Asians come from a variety of cultures and countries.
So in contrast to Austria-Hungary, where there were several well-defined ethnic groups with strong religious and linguistic identities, The US has only one significant minority group and a large set of small splinter groups who tend towards cultural and linguistic assimilation after a couple generations.