1. Corruption in Zimbabwe. Commercial farmers have been abandoning productive land and the country is getting poorer.
2. Communism in Cuba, Venezuela, SE Asia, and other regions over the past fifty years has ruined developing economies and made them worse. Most of those governments have fallen and things are improving again, but communism certainly has the power to ruin a country.
I'm sure there are others. Technological progress has give us a strong underlying upward trend around the world lately but sufficiently bad government can occasionally reverse the benefits of progress temporarily.