It's okay, you're not alone in suffering trying to get achievements with weak minors. I recently got the Battlecry achievement which is to conquer all of China and Japan as a warlord. Everything was going fine - until Communist China joined the Allies when it rose up. Since the achievement requires the territory to be fully annexed in a peace deal, I had to fight every faction except the Axis all at once, as the Guanxi Clique.
This meant:
To have any hope of defeating the Allies, the Axis needs to stay alive so the Allies are distracted in Europe.
To keep the Axis alive, I have to disband the Chinese United front and join the Axis to help them survive and win against the USSR. I also need to send as many planes as I can to Europe to stabilize the air war, which the Allies had won by that point in 1943.
Germany was on scraping the barrel by 1944 and I had to basically invade Japan, finish off the USSR, kick the allies out of Europe and the Med (and got lucky and trapped the entire Royal Navy in the Med, which let Vichy France naval invade the UK), and naval invade the USA all by myself.
It took until 1952 before I could get an achievement that should theoretically be relatively quick and only require you to beat Japan and the other Chinese minors.
Other highlights of the run: Non-aligned Portugal joining the Axis and then attacking Nationalist Spain, forcing Nationalist Spain into the Allies, me stealing the Japanese and Soviet navies so I would have any hope of reaching America, Italy falling into civil war, being almost completely annexed, coming back once Chinese troops arrived, and then Iraq blowing up and repairing the Suez Canal repeatedly because somehow they got the territory there at some point.
Historical focuses on by the way, and I took no ahistorical action as China up to the point where the PRC joined the Allies (aside from usurping the nationalists as GXC). I was just the leader of the United Front fighting Japan when PRC decided to go off the rails.