What dou think would have happend if germany and italy were united during the 1400?

During the 1400s? Wow, that’s super early.

Obviously, this would reshape European and Mediterranean politics rather dramatically – presumably the “Great Italian Wars” between the Hapsburgs and Valois would be mooted, for example – but it would really depend on how and by whom Germany and Italy were unified. Because a Germany united by the Hapsburgs is going to be quite different from one united by the Wittelsbachs or the Wettins, and an Italy united by the Papal States is going to look quite different from one united by Venice or Milan or Florence or Naples.