There were a number of processes that helped lead to the breakdown of feudalism in Europe. These processes were military, economic, and political. (Of course, it is very difficult to separate these three types of processes as each is in some ways connected to the others.)
Militarily, feudalism broke down in part because of changes in technology. Feudalism was built in part on the military importance of knights and castles. As time went by, technological changes made these things less important. The advent of the longbow and later of gunpowder made armored knights much less dominant on the battlefield. The invention of cannon eventually made castles obsolete. With these changes, the value of nobles and knights diminished and the feudal system was weakened.
Economically, feudalism broke down as trade and money became more important. In earlier times, countries’ economies were based almost completely on agriculture. This meant that control of land was paramount. It was easy for feudal lords to dominate their lands and to take tribute in kind from their serfs and other tenants. As time went by, trade became more important and the economies were based more on money than on barter. These economies were harder for local lords to control and their power diminished.
It is also necessary to note the importance of the Black Death. That pandemic caused the death of huge numbers of people, making those who were left more economically important. After the Black Death, peasants and other workers were able to demand better terms from those who employed them. This made them more powerful and it reduced the power of the lords and landowners.
Politically, lords became less important and the lower classes and the monarchs became more important. The economic and military changes made lords less necessary. Lower classes, such as merchants, became more economically important while mass armies made up of common people and controlled by central governments became more important. Thus, the need to have feudal lords diminished.
European feudalism changed with the emergence of stronger central governments, and the rise of the merchant class.