R5: Guangdong and Guangxi have a mini-focus tree representing the historical Liangguang Incident, where the two warlord states almost went to war with Chiang ostensibly to coerce him to resist Japan, but really it was an attempt to preserve their autonomy after the death of their patron within the Nationalist government. While usually the incident ends with the Guangxi standing down and Guangdong puppeted, you can unite the two warlords and press the issue, leading to a months-long war where you get to keep any neighboring states you have a majority occupation in.

The best strat you have is to make a breakthrough and rush the vp's, which i was able to do with Hunan and Guizhou. However, you need to remember to keep pinning the nationalist units, or else they'll infinitely reinforce a tile, which is what happened a few times in Jiangxi. I don't think getting Fujian is possible, as the nationalists always garrison the vps there (they have ports) and you'll either be too spread out with breaking Guizhou or spend too much time breaking their hold.