Much of it I suspect had to do with work. You wouldn't think to find a fairly large (percentage-wise) population of both Japanese and Greek ancestries in Idaho, but they were and are here. The Japanese came in the 19th Century to work on the railroad, and the Greeks were brought over in the 19th Century to work in mines in Utah; when the mines played out they too came to work on the railroad. Unlike the Irish and the Chinese, neither of these groups are usually thought of as railroad builders. Thus for many years Pocatello has had a Greek Orthodox church (it's on the National Register).

Likewise, Butte, Montana has the highest per-capita population of Irish ancestry in the US. They came to work the mines there. Many people of Finnish and Welsh ancestry went the to UP of Michigan and Northern Wisconsin to work the mines and in lumbering.