In my opinion, the disruption of trade is most likely the MOST severe effect that resulted in the fall of Rome. Trade has always been vital because every country has something special to offer weather it be oil, wool, wine, and a wide variety of food. Being able to trade with countries like Spain, France, North Africa, and the Middle East provided them a wide range of objects such as wool, tin, and lead. If their trade was disrupted, they empire would crumble at a fast rate due to a lack of supplies that were once vital. There would be less money coming through, and chaos would reign.
Hope this helps!