Complex sentence: The combined fleets of France and Spain had destroyed upwards of 100 merchant vessels, and made a great number of prisoners: part of whom were sent in a cartel to Halifax, and the remainder about 300 in number, were carried into France and Spain.
Split into simpler sentences: The combined fleets of France and Spain had destroyed upwards of 100 merchant vessels, and taken a great number of prisoners. Some were sent in a cartel to Halifax, and the remainder, about 300 in number, were carried into France and Spain.