Guatemala
Another small Central American country, just south of Mexico, with a grim 20th century history of bloody civil war, coups and death squads, and again – like El Salvador and Nicaragua – with a dark element of involvement of the USA in that dark history.
Apart from man-made tragedy, the country is also prone to natural disasters such as earthquakes and mudslides and has several active volcanoes.
As far as particular sites for dark tourists to visit are concerned I will have to do more research. So far I am only aware of a small civil war memorial at the cathedral in Guatemala City, as well as a memorial to the victims of the burning of the Spanish Embassy in 1980, located in the city's main square. But I am certain there'll be more. Once I've found out more details I'll post them here. Meanwhile I'd be grateful for any hints (contact me).