In 1896, when the Democrats and Populists merged, and with the fraying of the Republicans' Civil War coalition, the current wisdom was that a new period of Democratic hegemony was beginning. Marc Hanna disagreed.
The Populists were an agrarian party that was socialist on economic issues but biblical fundamentalist on social issues. They were anti-black, anti-Catholic and especially anti-immigrant.
The Democrats were already America's urban party and the natural home of first-time immigrant voters. But the marriage with the Populists now meant that the Democrats had to give up their urban advantage. Further, with people leaving the farms for the cities, the urban landscape with its immigrants was the place where elections would be won.
Hanna responded to the challenge by creating ethnic-American Republican clubs. He sent Italian, German, Polish and Lithuanian-speaking organizers into the cities to expedite getting immigrants naturalized and registered to vote -- as Republicans. This was a way of assimilating foreigners into the American way, by empowering them politically, teaching them the ropes and helping them wield power.
Hanna's plan worked so well it created a new Republican governing coalition that lasted until 1932 when the Great Depression destroyed it.
My late father's (Sicilian) side of the family was greeted by a Republican organizer when they came to Philadelphia in 1908 and promptly joined the local Italian-American Republican Club. They prospered during the Depression, so that side of the family is still staunchly Republican.
My late mother's (Neapolitan) side did poorly during the prosperity of the Twenties and even worse during the Depression, so they became (and still are) staunch New Deal Democrats.
As immigrants assimilated and moved to the suburbs, their interests and viewpoints changed, and so did their polical allegiances.
1. When Mayor Frank Fizzo switched from the Democratic to the Republican Party, he stated that it was a "homecoming to the party of his immigrant father."
2. When King Richard I of Chicago was looking for neighborhoods to bulldoze to build the U of Illinois at Chicago, he chose the near west side Tri-Taylor district. The reason being that the Italians who dominated the area did not vote for machine candidates and, despite being in a gerrymandered ward with Poles and blacks, still often voted GOP in local elections.