Why was the period from the late nineteenth the mid-twentieth centuries called "the golden age of parties"?

There are many reasons for that:

There was party stability, and the dominance of both Democrat and Republican parties was strong, which led to a big impact in the lives of millions of voters.The appearance of political machines, which were party organizations that incentivized people to join their party and increased their voter´s loyalty.Political machines became a central element of life for civilians.Political parties not only served the political needs of society, but also their needs for social services.