Complex sentence: On March 18, James Sawyer and his brother, Charles Sawyer, left England but Snell's parents, having learned of the plan, wouldn't allow him to leave, thus delaying his departure.
Split into simpler sentences: On March 18, James Sawyer and his brother, Charles, left England. But Snell's parents, having learned of the plan, wouldn't allow him to leave, thus delaying his departure.