In it’s current form the Starfleet Marine Corps is the culmination of generations of military history dating as far back as the seventeenth and eighteenth centuries on Earth. Within that history, the influences of a dozen worlds and species is sprinkled in, with the heaviest influences being that of Earth – the central hub of the entire Federation, and of Starfleet.
Ex Astris Scientia – “From the Stars, Knowledge.”. Starfleet is interested in exploration, discovery and enlightenment of the mind. It is, at its very core, a pacifist organization and, were it possible, it is presumed that they would carry no weapons at all. But, despite the Utopian aspirations of Starfleet and the United Federation of Planets, not every other species in the galaxy shares those ideals. Thus, Starfleet has armed its vessels, drafted binding accords to limit those military technologies that might do harm to others as well as the galaxy at large, and otherwise done only as much as was needed to defend themselves against those that might seek to take advantage of their curiosity or lack of aggression.
The SFMC is the antithesis to much of what Starfleet stands for as the knowledge sought from the stars is applied to combat, instead of diplomacy and expansion. Acquired knowledge is used to test themselves, to push the limits of their capabilities and in turn prepare the Corps for the next conflict. The SFMC is without question, a military organization whose sole purpose and existence is to protect the Federation from all enemies both foreign and domestic. Unlike their counterparts in Federation/Starfleet Security, who function as law enforcement within the Federation and Starfleet, the SFMC is primarily focused on combat. Their main function is to bring military conflicts to an end through aggressive combat action.