You and Goofy both said what I was thinking. Who would invade Haiti? There isn’t anything worth stealing. Therefore, Haiti doesn’t really need a “national defense” force.
More a matter of the “Roosevelt Corollary”: trying to keep European powers out of the West Indies…which control access to the Panama Canal, that Roosevelt had under construction. There was frequent US intervention in Mexico, elsewhere in Central America, Haiti, Dominican Republic, and others. For a while, Cuba was an official US “protectorate”. That all came to an end in 1934, along with putting the Philippines on a path to independence.
Steve