Complex sentence: As a result Spain had continued to govern the territory and refused Lewis and Clark permission to explore the territory forcing them to spend the winter of 1803-04 at Camp Dubois in Illinois.
Split into simpler sentences: As a result, Spain had continued to govern the territory and refused to giveLewis and Clark permission to explore the territory. This forced Lewis and Clark to spend the winter of 1803-04 at Camp Dubois in Illinois.