What contributed to the growth of the know-nothing movement in the mid-1850s?

The collapse of the Whig party.

Following the Kansas-Nebraska Act the Whig party fell apart. This left an opportunity for a new party to oppose the Democratic party. The know-nothings or American Party began electing their chosen legislators into office. This party was anti-catholic and famously aggressive towards immigrants.

Because broadest terms allows the law flexibility depending on changing society and circumstances.