Complex sentence: Initially membership in the Order was limited to officer veterans (and their hereditary descendants) of the Revolutionary War, the War of 1812, and the Mexican War and for the first two years of its existence membership categories were limited to veteran and hereditary companions.
Split into simpler sentences: Initially membership in the Order was limited to officer veterans (and their hereditary descendants) of the Revolutionary War, the War of 1812, and the Mexican War. For the first two years of the MOFW's existence membership categories were limited to veteran and hereditary companions.