I defeated France in two wars and got 5 of their provinces but now they are allied with burgundy and i cant defeat them both. So what should I do?
Never take provinces.
Make them release nations (Normandy, Champagne, Toulouse, Guyenne, Dauphine etc), and cancel their vassals. Much more effective.
Best would be if you found someone else for example Burgundy was allied with and declare on them, and then peaced out. And then declared on France. (Perhaps you could vassalize electors of HRE?....2 anyway, and offer vassalization to the monarchies)