Complex sentence: Mogador was an important harbour, the first seaport of Morocco, with constant relations with Europe, and had about 15,000 inhabitants, 4,000 of whom were Jews, and 50 Christian traders.
Split into simpler sentences: Mogador was an important harbour, Morocco's first seaport, with consistant relations with Europe. It had about 15,000 inhabitants, 4,000 of whom were Jews, and 50 Christian traders.