<span>The Know-Nothing Party was so popular that its candidates had been elected to important political offices throughout the United States. German-Americans, who were typically divided amongst themselves, united in their efforts to fight back against the discrimination directed at them. They were greatly aided by mounting tensions over the issue of slavery in the United States, which divided the Know-Nothing supporters and weakened them as a political group.</span>
Because they, as many other inmigrants, were catholic and on that time there was a anti-Catholisim movement in United States.
Explanation:
During that time (1820 and 1850) Protestantism in countries like United States and United Kingdom set the bases for radical groups which did not want any piece of Catholism in their lands. The radicals faced a problem when many inmigrants from Europe arrived to United States and wanted to keep practicing Catholisim, Germans included. This is why those groups like the Know Nothing promted hate and discrimination against German inmigrants.
