As I recall – mostly from watching Xavier’s videos – you have to complete 3 “liberation” missions in a region to get the mission to liberate the entire region. That’s a lot of investment in each region, so you need to pick and choose. There are also repercussions from doing many missions in a region.
But don’t take it 2nd hand from me, check out xwynns’ long war 2 playlists on youtube. He worked on the mod and is very familiar with its internal machinery.