The document summarizes the Roman conquest of Britain in three periods. First, it describes Britain before the Roman invasions, which was divided into tribes ruled by kings or queens and whose religion was guided by the Druids. Second, it explains Julius Caesar's initial invasion in the 1st century BC and his inability to fully conquer Britain. Third, it outlines the full invasion and conquest of Britain led by Emperor Claudius in the 1st century AD, after which Britain became a Roman province ruled by a governor.