Complex sentence: The Charlton Street Gang were one of the earliest river pirate gangs, raiding small cargo ships, in the North River, of New York Harbor, during post-Civil War period, of the 1860s.
Split into simpler sentences: The Charlton Street Gang were one of the earliest river pirate gangs. They raided small cargo ships in the North River of New York Harbor during the post-Civil War period of the 1860s.