Complex sentence: The tribe may have numbered as many as 10,000, but years of war with the French-supplied Hurons and exposure to infectious disease reduced their numbers and forced them west, first to the area between Saginaw Bay and Detroit in Michigan.
Split into simpler sentences: The tribe may have numbered as many as 10,000, but years of war with the French-supplied Hurons and exposure to infectious disease reduced their numbers. In response to these pressures, they migrted west, first to the area between Saginaw Bay and Detroit in Michigan.