What region does the 4th Marine Division serve?

The 4th Marine Division primarily serves the East Coast because it is a reserve division based in that region. The division consists of various units, including infantry regiments, and is tasked with supporting Marine Corps operations on the East Coast and beyond. Its structure allows it to mobilize and respond to needs both domestically and in support of active duty forces around the globe.

Other regions mentioned in the options do not accurately reflect the division's primary responsibilities. For instance, while the West Coast may host other Marine divisions and commands, the 4th Marine Division has its headquarters and reserve units specifically aligned with the East Coast. The South Pacific and Central America are areas that may involve Marine Corps operations but are not the primary focus of the 4th Marine Division's structure or mission. Thus, identifying the division’s association with the East Coast provides clarity on its operational scope and capabilities.