Complex sentence: Tryon's force forded the Saugatuck River well above Arnold's position, prompting Arnold's force and the chasing militia, now led by General Silliman, to entrap the British before they reached the beach.
Split into simpler sentences: Tryon's force forded the Saugatuck River well above Arnold's position. This prompted Arnold and the chasing militia, now led by General Silliman, to attempt an entrapment of the British before they reached the beach.