The three things that brought about the fall of Rome when they all hit at once are:
1. multiple civil wars
2. economic collapse due to inflation
3. repeated invasions from all over
Rome used to be the most powerful country that ruled most of the world, but over time, its strength started to wane. In the end, due to many reasons, such as these above, it was forgotten and gave way to new countries being created.
Federalism refers to the supremacy of he powers of state governments
