What factor led the temporary success of the know nothing party in the United States during the mid 1800s

The collapse of second party system.

Explanation:

The know nothing party flourished in he 1850's due to nativist movement, it grew due to anti-Roman catholic and anti-immigrant sentiment that became Rampant during 1840's.

Rising Irish migration in the East and the Germans in the west posed a danger to the political and economic security of the native born Americans and american values as they were controlled by the pope. This movement tried to curb naturalisation and immigration from 1854-1856 but it couldn't succeed.

It was known a American party from 1855 onward.

Historians the collapse of second party system was also the key factor to its success because it gave the opportunity to succeed where the older nativist group failed.