The largest and deepest dataset, absolutely, but raiders and traders blurred those boundaries even before modern transport technologies. Y-chromosomes in eastern England: at least 50% are indistinguishable from stay-at-home Germanics on the Continent. And 10% are Norse.
I also have grave suspicions about "didn't interbreed" in the context of pre-20th C British. Didn't intermarry? Perhaps. Didn't interbreed is lol, esp if they had money.
Most English settlers didn't have money, but there were so many of those its hard to believe they didn't leave a larger genetic footprint. This map has about as much English as I'd expect in Columbia, not one of Australia's siblings.
Open to what you say on intra-US migration, but I'd really like to see data.