What about generalizing "western" history? There are significant trends in history like the Enlightenment, Renaissance, early Industrial Revolution, the rise of Protestant Catholics, the collection of countries who worked together in the Crusades, etc, etc that crossed regional boundaries like England, France, Sweden, German, etc but were still very much a homogeneous definable group among a wider Western population. Whose societies were very similar and evolved on a similar and distinct trajectory.
Even extending across continents from Europe into North America and South America, where simply using countries is to ignore plenty of higher-level context and wider cultural trends.
Not to mention the mixed European heritage of early North Americans, which developed an identifiable wider culture (even if much of it was built on top of slavery). Or the fact even England was largely a mix of Celtic, Scandinavian, Roman, etc which can be distinguished by going back in history but merged into one culture over time, much like America did.
I get the flaws, risks, and hostility to lumping them all into "white" though, so I'm in agreement there. All analysis requires context and race is a very poor category to work with. Even the neo-nazis and Hitler seem to struggle to define what "white" means and invent categories like Aryans, to exclude obviously white people like Slavs.
But still the human brain largely works via patterns and lumping groups into categories, whether that's socially acceptable or not. So even if it's not ethically "right" I can still see why it's such a common phenomenon, despite being a poor categorization.
We should all be using cultures rather than race, ethnic group, OR country/geographic area.
"Albion's Seed" or "American Nations" should be required reading for anyone obsessed with race to really understand the flaws of racial categorization:
It should even be in high school history education IMO.