Why might political revolts slow development?
If you are talking about economic development, I would say that political revolts slow it because they destroy infrastructure and because they make people feel uncertain about the future of a country.
The first of these is pretty obvious. If your country has oil and a rebel group destroys pipelines that carry the oil, your country's development will slow down.
The other is less obvious. Let's say you have a bunch of money and you want to start a company or invest in someone else's company. Will you really want to do this in a country that is having political rebellions? I think that you would worry that the rebellions would end up destroying the company and making you lose money. So you would invest somewhere else and the country with the rebellions would not develop.