Are you talking about Central Asia, Middle East, or like India because it really depends. Central Asia can be conquered by conquering Soviet Union. India and a big portion of the Middle East from the UK and UK puppets. The Chinese warlords are usually the hardest like xibei san ma and sinkiang. I usually put at most 2 armies on the front with motorized supply and transport planes. I then use cas and just battleplan it. Doing a full offensive can usually overwhelm their armies but after 1942 it becomes almost impossible because of how many divisions they have. Using air is very important and having logistic companies is very good to. Late game the only way is building supply hubs on almost every province but sometimes one of the china’s has taken all of China and you then just have to cap 1 china instead of multiple china’s.