Final answer:
Power shifted from kings to nobles in medieval Europe because nobles often had more land and power than the kings and could thus challenge royal authority. The feudal system enabled nobles to gain this power, but by the end of the 14th century, monarchs began centralizing power, starting to reduce nobility influence.
Step-by-step explanation:
Power in medieval Europe shifted from kings to nobles primarily because many vassals had more land, wealth, and power than the kings themselves. As a result, these powerful nobles could challenge or ignore the authority of their monarch, potentially leading to conflict. During the medieval period, the feudal system arose out of the need for security against raiders and the lack of more effective forms of governance. Under this system, lords would grant lands to fighters, who became their vassals and owed military service in return. Over time, the monarch's role was diminished as they granted lands and privileges to placate their lords, thereby weakening royal power and authority.
By the tenth century, kings and nobles had reimagined the Roman Empire's idea to serve their purposes, creating a society based on a combination of Roman, Christian, and Germanic traditions. Through advantageous marriages and other strategies, they sought to maximize their resources and influence. However, it wasn't until the end of the fourteenth century that England and France began to create centralized nation-states, which started to reduce the nobility's power.