Article: In Latin America in the 1970s, leftists acquired a significant political influence which prompted the right-wing, ecclesiastical authorities and a large portion of the individual country's upper class to support coup d'états to avoid what they perceived as a communist threat. This was further fueled by Cuban and United States intervention which led to a political polarization. Most South American countries were in some periods ruled by military dictatorships that were supported by the United States of America. In the 1970s, the regimes of the Southern Cone collaborated in Operation Condor killing many leftist dissidents, including some urban guerrillas. However, by the early 1990s all countries had restored their democracies.

Now answer this question: The regimes in the southern cone collaborated in killing of who?
leftist dissidents