Complex sentence: Revere did not shout the phrase later attributed to him ("The British are coming!"), largely because the mission depended on secrecy and the countryside was filled with British army patrols, and because the colonists themselves were British.
Split into simpler sentences: Revere did not shout the phrase later attributed to him ("The British are coming!"). His mission depended on secrecy, the countryside was filled with British army patrols, and the colonists themselves were British.