First a reminder and warning the Condor operation is a sensitive subject that subject we know relatively little about. Several governments still haven't opened their archives so the information we have are partial. There is still some difficulty in investigating this time period in several of the involved countries as people still fear the return of the dictatorships and the amnisty laws in place may keep the people directly involved free from inquiry. We also need to remember that the people that lived through this period are still alive, both the tortured and the torturers have to coexist and some times they are the ones writting and researching history. It was only recently that the existence of the operation was officially acknowledged.

Three countries, that I know of, that have managed to more or less open their files and attain some justice: Chile, Argentina and Paraguay. Most of the data come from them or the USA declassified documents.

Incidentaly, the treaty that officially created the operation was signed in Chile, 5 of november of 1975, in the "First Inter-American Meeting of National Intelligence". Officially the reason of the meeting was creating a Coordination Center in Chile, not unlike interpol but focused on subversion. They believed, as Contreras put it and John Dinges emphasized in his book on operation Condor:

Subversion, [he wrote], . . . does not recognize borders nor countries, and its infiltration is penetrating every level of national life. Subversion has developed a leadership structure that is intercontinental, continental, regional and subregional.

As examples we can list the Tricontinental Conference of Havana, the Revolutionary Coordinating Junta [JCR] for South America, etc., all of which are given a pleasing face by all kinds of solidarity committees, congresses, Tribunals, Meetings, Festivals and conferences, etc.

In contrast, the countries that are being attacked on the military, economic and political front (from both inside and outside their borders) are fighting back at most only with bilateral understandings or simple “gentlemen’s agreements.”

Now, It's important to understand why he thought like that you need to know that the military from all the involved countries had men that studied in the School of Americas. There they learned the National Security Doctrine (NSD). In practice this doctrine redefined threat so as to encompass internal movements and Sovereignty so as to be associated with the keeping of order. That Doctrine allowed the military to view it's people as the enemy and freely attack them. In the School of the Americas the idea of the communism as a enemy was also planted and spread.

The NSD lead to the understanding that there was a new war unlike the traditional one this wasn't a war for territories it was a war of ideas. This new war had no borders and the enemy was invisible, difused and permeable. So it was necessary a new form of organization to fight it.

It is important to say that the countries had, prior to november 1975, already done more than on bilateral operation among themselves, as insinuated in Contreras affirmation. They had some experience working together and saw the great results they could attain via cooperation. The next step was almost natural.

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The books that I used as sources:

A 40 años del cóndor: De las coordinaciones represivas a la construcción de las políticas públicas regionales en derechos humanos. Published by the "Instituto de Políticas Públicas en derechos Humanos del Mercosur".

Dinges J. THE CONDOR YEARS: How Pinochet and His Allies Brought Terrorism to Three Continents. 2004.

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Some texts and books if you want to learn more on the subject:

McSherry, J. Patrice. PREDATORY STATES: Operation Condor and Covert War in Latin America.News Article: Bolsonaro é o primeiro presidente a admitir a existencia da Operação Condor

Official Site of the Comissão Nacional da Verdade

Cerveira N. M..ASAS DE SANGUE O VÔO DO CONDOR SOBRE O BRASIL (1973/1985). 2004.

In the National Security Archives you will find several articles and documents to read online in english.

I don't know which languages you speak so I put texts in spanish and portuguese too.

Edit: I just realized you wanted recommendation on the whole of the Cold War not only operation condor. Here some extras :

Pastor R. A. & Long T. THE COLD WAR AND ITS AFTERMATH IN THE AMERICAS: The Search for a Synthetic Interpretation of U.S. Policy. 2010.

Blanc J..Itaipu’s Forgotten History: The Brazil–Paraguay Border Crisis and the New Geopolitics of the Southern Cone. 2017.

Filho P. P. O Itamaraty nos anos de chumbo – O Centro de Informações do Exterior (CIEX) e a rep ressão no Cone Sul (1966-1979). 2009.

Fernandes A. S. A política externa da ditadura brasileira durante os “anos de chumbo” (1968-1974): as intervenções do “Brasil Potência” na América Latina. 2010.
Moniz L. A. Brasil, Argentina e Estados Unidos: Conflito e integração na América do Sul. (I believe this one has a translation but I am not sure.)