What is political and economic transformation of Western Europe after the fall of Rome?
How did the organization of Medieval European societies differ from that of Rome at its height? Look to discuss Decentralization/Self Sufficiency.
One of the best examples to illustrate your comment after your question is to look at Roman Britain between the building of Hadrian's Wall 122 A.D. and 476 A.D. The Roman Empire in the west had been slowly fracturing for many years and the legions showed signs of demoralization. This led to power struggles, which led to a weakened army, and was compounded by the rising strength of the clans in Britain. Some soldiers just left their western posts, however some of the soldiers that stayed in Roman Britain actually became quite well off. There evidence that suggests that the men of the legions that stayed became what later becomes known as the first nobles, along with the strongest of the Britain clans. Ultimately this strange relationship gave way to a sort of mixing of the power. Those of the Roman military still had might and for the most part superior fighting skills, those of the clans had territorial and a patriotic autonomy. Politically the leaders of both groups served a purpose for the rest of the people...the people needed protection and were willing to pledge their support primarily through a new economic relationship with these new leaders. This new relationship was based upon a political and economic exchange between those who gained power and retained power and the masses that surrounded them, this exchange was not dominated by the Roman empire but by smaller, more self sufficient, and decentralized societies prompting the early stages of individual kingdoms that would come to dominate western Europe.
With the fall of Rome, an empire came to an end. In other words, all the benefits of an empire were over. This would include, good functioning communication, broad infrastructure, such as roads, a centralized taxation system and even safety to some extent. What came to pass instead was a number of groups, such as the Franks, Goths, etc. These were independent groups that often fought each other. Eventually all of this lead to feudalism and more independent kingdoms.
This is a pretty big question, and the answer is not the same for every time and place after the fall of Rome. But in general, the ideas of decentralization and self sufficiency go a long way to describing what happened.
After the fall of Rome, Europe split up into all sorts of little political entities. Where Rome had once ruled a large part of Europe, it now came to be ruled by "nobles" who controlled as much land as they could.
Self-sufficiency became more important after the fall of Rome. Now that Rome did not control everything, it became very dangerous to travel and, therefore, to trade. There were too many people who might steal a trader's goods and money. So there came to be much less trade and areas needed to be self-sufficient.