Complex sentence: The French force was stretched too thin defending the whole river bank and broke at several points and allowed the English to enter the city and attack the bridge defenders from the rear, prompting a collapse in the city's defence.
Split into simpler sentences: The French force was stretched too thin in defending the whole river bank and broke at several points. This allowed the English to enter the city and attack the bridge defenders from the rear, prompting a collapse in the city's defence.