How can a country be unstable?

I'm pretty sure that a country can be unstable if there were a lot of deaths, if there weren't enough kids who had educated, or if there weren't that many men and women who didn't have jobs so they couldn't send their kids to school. It can also be unstable because of debt, bad economy, and health issues. 

A country can be unstable in a lot of ways, i.e debt, bad economy, no educational system, no way to address health issues/medical,no jobs