United States train travel had changed dramatically by this time, since the transcontinental railroad had been completed, which stretched all the way from the Atlantic to the Pacific
The answer is: Political bosses expanded their power by helping immigrants in return for their loyalty.
At that time, many of the political bosses realized that if they somehow can help the immigrants obtain their citizenship, the immigrants will become much more likely to return their favor.
This mean that they can influence the immigrants to vote for them during the election in exchange for the citizenship. This help the political bosses expanded their power.
They possessed large amounts of raw materials
