The collapse of the Western Roman Empire was a traumatic event in the history of Western Europe, seen from the future. However, at the time the events were unfolding, many social and economic events were occurring over many years that transformed what once was a stable Roman society.
The times of the 5th and 6th century AD saw trends such as population decline (specially in urban centers), a decline in trade, and increased migration of peoples. Before the 5th century AD, the Pax Romana had provided stable conditions for the flourishing of cities, and trade between different regions. People did not need to migrate massively.
The lack of the authority of the Roman empire led to the vanishing of the administrative, military and educational infrastructure. Literacy declined and with it, the practice of systematic agriculture. This, led to famine and population decline. Things were made worse by the Plague of Justinian, which led to a 40-50% population loss in Europe between the years 541 and 700 AD.
The use of money declined compared to the Roman times. It was replaced by a barter economy
In summary, the early Middle Ages were a time of change, with many economic difficulties for the inhabitants of Western Europe at that time.