Do you mean to ask if Europe was defended overall under the Feudal system? Because, if so, then no. The Feudal system allowed for a hierarchy of social castes that allowed the rich or royal to get richer and more powerful, while keeping the serfs, commoners, and lower ranking leaders in their places.
While this was great for dealing with power struggles between kingdoms, everyone was clearly delineated in their places and the commoners were often separated from the more important aristocrats, it did often lead to outside threats either being ignored, foolishly, or dealt with slowly. Europe's main strength that led to its rise in power? Technology. Especially military technology.
