Nullification is the process by which the government uses it's power to invalidate a pre-existing law. In the case of the regulations that required people to own land in order to vote, state governments were able to eliminate those requirement by using the Constitution to defend their choice. This process was introduced by Calhoun's Theory of Nullification.
The most straightforward theory for Western Rome's collapse pins the fall on a string of military losses sustained against outside forces. Rome had tangled with Germanic tribes for centuries, but by the 300s “barbarian” groups like the Goths had encroached beyond the Empire's borders.
