In the late 1840s, Philadelphia's Irish population numbered in the tens of thousands, many of whom had immigrated to the city after the Irish potato famine of 1846-1847. Large segments of this local population firmly believed in Irish nationalism and were willing to fight for it. Nationalists movements such as the "Young Ireland" movement of late 1840s and early 1850s, served as inspiration for their cause.

 

A branch of the Fenian Brotherhood had been established in Philadelphia by the 1860s, and the city hosted the Fenian's first national convention in 1863 during which a Philadelphia printer by the name of James Gibbons was elected director of the organization. Interesting plans were laid at that convention that involved recruiting Irishmen from the Union Army in preparation for future military actions against England.

 

The Fenian Brotherhood in the U. S. was eventually superseded by Clan Na Gael, which took up the fight for Irish independence in 1867.  The brotherhood continued some underground operations, but slowly dissolved over the course of the 1870s and 1880s.