If you are talking about Western Europe during the Middle Ages after the fall of the Roman Empire, there are several ways that the people of the times managed to maintain some sense of stability.  First, the church took over much of the power vacuum left by the fall of the Roman Emperor.  Monasteries helped to maintain stability in rural areas, and Bishops became powerful secular authorities as well as religious authorities within cities.  With the lack of a central political power, a complex network of relationships developed to maintain both the military and the economic sectors of Western Europe.  The feudal system of relationships between knights and Lords in return for land or other financial support helped larger landowners protect their land.  A complementary system called manorialism was developed to protect and utilize the crops grown on the land.  In this system, peasants farmed for the Lord on his land in return for land to farm on their own as well as protection from outside invaders.  The system was actually a hodgepodge of duties and responsibilities for both sides.   Eventually, a system of nation states grew up and replaced both the feudal and manorial systems resulting in the nations of Europe that we know today.