Complex sentence: The Susquehannock nation remained independent and not part of any confederacy into the 1600s, but they were not strong enough to withstand the competition from colonists and other tribes in the wars of that century.
Split into simpler sentences: The Susquehannock nation remained independent and not part of any confederacy into the 1600s. They were not strong enough to withstand the competition from colonists and other tribes in the wars of that century.