These two men seated at the table represent the Irish , with top hat and vest, and German (smoking pipe and drinking german beer) inmigrants in the 1800s in the US. The cartoon refers to the 1882's Chinese Exclusion Act, which was the first American law preventing the inmigration of an specific ethnic/national group. This can be apreciated in the "New Declaration of indepence" at the back of the cartoon.
The legend in the bottom ("If the Yankee Congress can keep the yellow man out, what is to hinder them from calling us green and keeping us out too?") refers to the raising fear in Irish and German groups of facing the same fate of Chinese inmigrants. This let us know American attitude towards inmigrants who weren't seen as equals and were discrimitated for their origins and skin color.
The answer is <span>It allows readers to approach a “forbidden door.” </span>
