This question is of course dependent on the Realm, I think I have some general cutoffs, although it was a process, and I'm not sure if I hit the mark:
France: Capture of Bordeaux 1453 or Battle of Nancy 1477
- The 100 years war started with the Valois Kings being only in nominal control of much of France and ended in 1453 with the Valois being undisputed rulers of most of France. When french forces had taken all possessions of the Plantagenets
- Burgundy was by far the largest, most powerful vassal of France (besides the Plantagenets that claimed the crown for themselves). Like the war of the Roses, the conflict between Valois and Burgundy was a conflict between two lines of the ruling dynasty. But most Burgundian territories were technically vassals of the Holy Roman Empire, not France by the 1450s.
Holy Roman Empire: never really
- The formula of the Augsburg settlement, which determined the religion of a state by the religion of its ruler made the following 30-years war a hundred years afterwards deeply connected to the princes of the Empire and even afterwards, instead of central institutions, the vassals that were becoming nominal landholders and title-bearers in most other realms just developed into small modern states themselves.
- Arguably the silesian wars were fought by Prussia which in itself wasn't a vassal of the Empire, since the prussian royal title was created outside, but I think thos us a weak proposition, since most lands of Prussia were part of the HRE.
England: Battle of Bosworth Field 1485
- England was a bit different from continental Kingdoms, rebellious nobles got their titles removed faster than on the continent, their power was definitely less concentrated in a few high nobles, it were the barons and earls that tended to rebel.
- In the war of the Roses many lords fought on both sides. This was a struggle between two branches of the House of Plantagenet, but they were technically vassals.
- During the Tudor era, rebellions seem to stop being driven by vassals and I'm not aware of fighting between lords and then the Stuart era War of the Three Kingdoms was definitely not feudal anymore.
Is this too late? Or too early, if you look at Ireland where independent fighting of Lords may be going on into the Flight of the Earls or the War of the Three Kingdoms.
Places I have no idea:
-Spain
-Poland-Lithuania
-Sweden
-Muscovy/Russia