Complex sentence: He was engaged in the Dutch merchant service from about 1655 till 1659, and then bought a vessel with his savings, and with a band of reckless men, whom he had enlisted, became a terror to the commerce of the Netherlands.
Split into simpler sentences: He was engaged in the Dutch merchant service from about 1655 until 1659, and then bought a vessel with his savings. With a band of reckless men whom he had enlisted, he became a terror to the commerce of the Netherlands.