Complex sentence: The colonial charters for New York and Massachusetts both described their boundaries as extending westward to the Pacific Ocean, but used distances from coastal rivers as their baselines, and thus both could claim the same land.
Split into simpler sentences: The colonial charters for New York and Massachusetts both described their boundaries as extending westward to the Pacific Ocean. However, both charters used distances from coastal rivers as their baselines, and thus both states could claim the same land.