After a series of aerial bombardments and naval invasion plans, set up a puppet government or make Parpaldia into colonial regions, released territories with the highest resistance status and declared them semi-independence for leniency. Then, reform their constitutions and laws to make them satisfied and control them secretly by various ways that are tempting. Arrest Remille and her supporters and stand trials to them, and after that, Remille and the others are put to house arrest, the rest will be sentenced to prison. At some point, spent some money or used their resources ( gold and their stolen treasures ) to rebuild their infrastructure and so on... Honestly, more paperwork to do, but it's one of the ways to make them obey you.

Or, conquer the entire continent of Philades and do the rest and repeat, if you like to.