As Prohibition looms on the horizon, the Milwaukee city council realises that their beer industry, the biggest in town, is about to go belly up. So they invest in ... hmmm... engineering?
A senior Japanese engineer comes to Milwaukee, building, say high performance car or maybe Aero engines.
maybe he's got a grandparent who was korean or untouchable, and he KNOWS he wont rise far in Japan. He succeeds, and convinces a bunch of his former coworkers to come join him.
Word gets out around japan, that if you are untouchable, or ofkorean ancestry, you can go to milwakee, and get a good job.
Meanwhile, california has a spate of anti oriental violence and prejudice. The Japanese community there, being smaller and more spread out than the Chinese, suffer diproportionately. They, too, hear of opportunities for hard working japanese in milwaukee. Interestingly, this leads to an inversion of the usual japanese social structure, as it is people with untouchable and korean relatives who get the best jobs, while the 'pure' japanese are often manual labourers.
Come wwii, the japanese community in milwaukee is the biggest single such community outside hawaii, and is desperately and visibly proAmerican. Moreover, they are now deeply integrated into one of the major defense industries.
When japanese in hawaii and the west coast are herded into detention camps, the japanese in milwaukee move into defense industry compounds, with company supplied housing. Yes, its a step down from what they had had, but they are valued, even if carefully watched, workers.
The disparity in fates means that any exHawaiian or exCalifornian japanese with decent jobs try to move heaven and earth to get their relatives out of the camps and to milwaukee.
The politicians from milwaukee push washington for this, as the want a good supply of cheap, motivated labour for their booming war industry. Politicians from the pacific states are happy with this, as it gets rid of a bunch of detainees from their hands.
By the end of the war, there are more japanese in milwaukee than even in honolulu.
How is that?