In the US the final frontier is radicalized neo-confederate theocratic white Christian nationalist rural America that threatens the system's democratic legitimacy through institutionalized minority rule through an unrepresentative, rural-tilted senate and constitutional immobility. Throw in no term limits on the politicians in robes Supreme Court for good measure. If the American empire implodes, it won't be because of the drain of treasure and blood on its Baltic or Indo-Pacific frontier, but from the institutional rot within.