Complex sentence: Slobbery Jim (real name unknown) was a leader of the 1850s New York City gang, the Daybreak Boys, which was was formed in the late 1840s in Five Points slum with membership drawn from teenaged Irish immigrants.
Split into simpler sentences: Slobbery Jim (real name unknown) was a leader of the 1850s New York City gang, the Daybreak Boys. The gang was formed in the late 1840s in the slum of Five Points with membership drawn from teenaged Irish immigrants.