Complex sentence: During the War of 1812, a local citizen militia in St. Mary's County established a clandestine base on Point Lookout to monitor movements of British warships on Chesapeake Bay.
Split into simpler sentences: During the War of 1812, a local citizen militia was organized in St. Mary's County. They established a clandestine base on Point Lookout in order to monitor movements of British warships on the Chesapeake Bay.