US whiteness is a social construct that serves to justify and reproduce marginalization: white supremacy. It started out excluding the Irish, Italians, the Spanish, Slavs, etc and shifted over time in order to maintain anti-blackness and anti-indigeneity. So it is far from just one thing and is simultaneously very recent. It would be best described as a culture of domination and capitalism, being a product of the US’ industrialization and then economic subjugation of the planet. Whiteness is about who you are better than and how entitled you are to a good life, or at least one better than non-whites. White culture is tolerating and even engaging in genocide so long as it is against non-whites. White culture is trying to pretend oppressions don’t need justice on any timeline that might inconvenience a white person. White culture is jingoist. The image of a warlike America has a white face.

As white people were largely drawn from European immigrants, they sometimes have watered-down elements of culture from “the old country”, Americanized to the point of being unrecognizable. Those elements were usually watered down because their immigrant ancestors were not considered white at the time so they tried to hide or erase identifiable cultural elements. Name changes. Modifications to food. Going to the whiter church. Skipping traditional holidays.

And of course, much is just white supremacy under capitalism. Processed industrialized foods. Commercialized holidays and events. Workaholic myths of paths to success. Everything cheaper or subsidized to their benefit and treated as an entitlement. National chauvinism and racist warmongering. Colonizer mindsets.