Complex sentence: It was the headquarters of the Huguenot rebellion of 1621, and was vainly besieged by Louis XIII for eighty-six days; nor did it submit until after the fall of La Rochelle in 1629, when its fortifications were destroyed by Cardinal Richelieu.
Split into simpler sentences: It was the headquarters of the Huguenot rebellion of 1621, and successfully withstood an 86-day siege by Louis XIII. It did not submit to royal authority until after the fall of La Rochelle in 1629, when its fortifications were destroyed by Cardinal Richelieu.