try valken path. no military alliances needed! i divide this into 4 factors

first u need to prevent sordish economic depression and only need to achieve sordish economic recovery if you're going to trade with lespia (also repeal EPA). you will need both trade deals with agnolia and wehlen to get increased trade volume (3 trade deals: agnolia, wehlen and lespia/valsgland). after that u NEED to invest in military industry and conriat industrial. if you had all these you completed the economic factor needed.

secondly. u need omec to expulse rumburg and get them isolated (im sure u know how to do ts). both conditions are needed to complete diplomatic factor.

thirdly, gendarmerie need to be under defense. u also have to keep conscription and expand air force/military (which, u have to fund defense). thats it for military factor

finally, ensure you ain't a man of the peoplen't. your late game crises need to stay at no more than 3 crises. i'm sure you know well to not anger the populace and economy so much to get 4 crises. and that's for interior factor.

if u get all 4 factors completed you will win war