Peasant revolts in England, France and Spain were quickly quashed, but still gave peasants a sense of sovereignty. Further, peasants commanded higher wages and kings gained legitimacy and power. Lords were squeezed by a variety of other factors on all fronts. Towards the end of the middle ages, this led to centralized power and the end of the distributed feudal system.

During periods of war, kings would often rely on mercenaries, paying them to participate in individual skirmishes. However some of the most violent periods came during peacetime when heavily armored men were no longer getting paid, and so set to indiscriminately plunder the countryside. This resulted in an increasing practice of royal standing armies, strengthening royal power and reducing reliance on knights.

Technologies reducing noble power:

• Cannons: rendering their own castles less effective, less security at home.
• Longbows and gunpowder: rendered their offensive capabilities less effective, rendering them less effective offensively.

With dwindling military effectiveness of knights, there was no longer need to amass large knight armies, or for the feudal system at large. Cannons were prohibitively expensive, so could only be acquired by kings.

Thus the feudal noble class was squeezed out of existence, and many nobles became salaried courtiers employed by kings.

Source: High Middle Ages, Late Middle Ages, Medieval Technology and Social Change by Lynn White