Complex sentence: The name of Michillimackinac (later abbreviated to Mackinac) was applied generally to the entire vicinity, as well as specifically to the post at St. Ignace--and, later, to the fort and mission established on the south side of the Strait of Mackinac.
Split into simpler sentences: The name of Michillimackinac (later abbreviated to Mackinac) was applied generally to the entire vicinity, as well as specifically to the post at St. Ignace. Later it was applied to the fort and mission established on the south side of the Strait of Mackinac.