One of the reasons the military has so many independent branches is that it would take all of them to rebel and join the opposing side in order to win. It's impossible to tell how they would side in a real internal conflict and the whole apparatus probably has to break down first before they will ever officially take sides of a force that opposes the federal government. At that point there will be total chaos and the wealthiest people can once again swoop in, amass the most powerful force and take over.