As of the end of Endwalker...
Garlemald is already under the control of a foreign military: The Ilsabard Contingent, many of which are citizens of former provinces. Post-patch content will probably involve the Ilsabard Contingent and possibly transferring power to the Garleans. But right now, if any foreign force attempts to invade Garlemald they'd be faced with the Eorzean military and not the Garlean one so it would probably end up in talks rather than military conflict. All-in-all, it reminds me of Occupation Era Japan when the US military was in full control of the country for a few years.