A lot of bad things can happen. One reason is that if they don't fulfill their civic duty, we wouldn't be having elections and their would not be any leaders. This is especially bad because the U.S. is famous for it's leaders and it's freedom. I myself is a immigrant and is very fond of this country. That is one reason of many more.
If people did not fulfill a civic responsibility, the world would be a mess. An example is picking up trash. Picking up trash is not an obligation, but people do it because it’s their responsibility. If nobody picked up trash, the world would be a literal mess. There would be trash all over the ground and water. Lots of animals would die because they might eat trash their not supposed to eat or they might get stuck in trash. If people did not fulfill their civic obligations/duties, then they might be fined, spend time in jail, and there are other punishments too. (I could think of an example but this already seemed kind of long so I didn’t write it.)
At the end of the French and Indian War or the Seven Years War, the British lost most of their land west of the Appalachians and there was no place for new colonists to go.