I would restart and than adapt a very aggressive playstyle in which you conquer really fast the surrounding areas. Passive playing only corners you and makes the enemy overpowering. Maybe you could reload an earlier savegame, conquer every province except one, build a lot of gold mines and than collect enough money until you are pleased.
Than you take the money with you in the next chapter and buy yourself a big enough army to conquer the provinces and create a stable position to win the war.
I hope my ideas are helpful for you
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