I grew up in city with virtually no "minorities." A city of 50,000 that was almost all white...one black family that I didn't know existed because they lived on the opposite end of town. There was a mix of English, German, Norwegian, Irish, Bohemian, and a few other ethnicities considered white. I'd be hard pressed to tell the difference in the behavior of any of the children and adults of those "white" groups.
So are European descendants one "race"? I don't know. I'm not a big believer in race as many "race realists" believe. But I am aware there are large differences in group behavior.
I am missing or misunderstanding some points of your comments. I grew up as a depression ‘poor’ youth in the years before WWII. My brother,who died in the battle for Okinawa, and I played with and were teammates of boys from several ethnic backgrounds. Of special note was our relationship with “black’ people who we came to admire as a neighbor and family friends. Whether you think of such differences as not being of different ‘races’ is your take. Later in life after service in WWII including overseas I had very close relationships with Chinese and other what I called cultural groups. I never despaired about thinking/believing that in my lifetime I have had good friends from what I considered different ‘races’. My life’s experience tells me that denial of ‘race’ is like denying there was ever a Tower of Babel.