A few years later, the English Sea Power defeated the Dutch ending their continued influence in North America. The Conestoga continued to grow in strength. In the 1660s, the area supported a military conquest which greatly weakened two of the western Iroquois tribes: the Seneca and Catagua. They were also struck by three years of plague (around 1670) in which 9 out of 10 Susquehannocks died. In the next few years, renewed war with the Iroquois kept the tribe from recovering and only a pale remnant of its strength relocated to the plains area now between Harrisburg and Philadelphia, where they came to deal with William Penn and the new colonial Province of Pennsylvania.