We have a lot of both hilarious and terrifying facts about the Cuban Missile Crisis that turned up after the fall. First the actual negotiations that lead to deescalation came about by accident. The story in the west is that an American reporter (John A. Scali) met a Soviet diplomat/spy (Alexander Feklisov) who was sent to established a channel for negotiations for the withdrawal of missiles. But records show that Fekilsow had no directives to negotiate, and in interviews he claims that it was Scali who initiated the negotiations. Scali denies this though. The most likely explanation is that they misunderstood each other, and the deescalation started by accident!

Thereafter Soviet removed their mid range nuclear warheads from Cuba that CIA had detected by aerial photo. They also removed the long range nuclear warhead that CIA had no idea about. The Soviets simply assumed that those where discovered as well.

Finally we come to the question of why Soviet deployed nuclear missiles in Cuba. CIA had many different theories, but none of them turn out to be true. In fact there was no specific thought in the Soviet administration about placing nuclear weapons close to American soil, it was just part of a standard package for strengthening the military capabilities of communist allies.

Another thing that became apparent when the archives was opened up was that the western powers vastly overestimated the unity between the various communist nations. Specifically Soviet and China. Interestingly this misconception was mirrored on the other side in that the Soviets overestimated the unity of the western powers, and was unaware of conflicts between USA, GB and France for example.

Speculating a bit, this mutual overestimation of the other sides unity was probably a large factor in keeping the Cold War cold. Source: Underrätelseanalysens metoder och problem, Wilhelm Agrell. and lectures by Wilhelm Agrell.

The partial opening of the Soviet block archives shed some light to Soviet decissionmaking and the main surprise for Western cold war historians was that they were using the same language to justify decissions internally as they did externally in their press. Just as the American policy makers had faith in the theories of Rogov on "modernization" requiring a strongman to hang all the communists on palmtrees their Soviet counterpart had faith, for instance, that their support for some "bourgeois nationalists" in the third world would help to develop their local "material forces of production". It was not an evil empire best understood with some "realist" wisecracks about totalitarianism and power for the heck of it but by reading Marx, Engels and Lenin. They were about as benevolent as their American counterpart.

source: second tome of the Cambridge History of the Cold War by Odd Arne Westadd and Melvyn P. Leffler

A little late to the party, but if you're interested in this topic, I would HIGHLY recommend "The Haunted Wood" by Alexander Vassiliev and Allen Weinstein.

The Haunted Wood is a cooperation between the US and Russia post-Soviet collapse to disclose intelligence records of the KGB on Stalin-era espionage activity.

I'll try to organize the rest of this post so that it's a little easier to read and digest:

##Joseph McCarthy:

One of the most interesting things I got out of the book was the general premise Joseph McCarthy was trying to push regarding the number of Soviet spies in the State department was more or less spot on.

The first few pages of the book are devoted exclusively to listing the Soviet assets with their true and code names as well as where they were positioned in the US government.

McCarthy who has been condemned for "witch hunting" gave rise to the renewed concept of "McCarthyism" or making a career out of accusations of others. Although his method of execution was extremely self-serving and a bit disorganized, he was essentially right. The Soviet intelligence apparatus had spent extensive resources to tracking and collecting human assets within the US government by leveraging socialist sympathies to recruit agents.

It turns out that method was effective and resulted in the US State Department being filled with Soviet informants for most of the 30's and 40's.

##Alger Hiss:

One thing that isn't appreciated as much today is the amount of uncertainty that surrounded accusations of Soviet espionage. Today we tend to think of most of the people painted as Soviet spies as guilty beyond reasonable doubt, but only because we have records now showing clearly who was actually responsible.

Alger Hiss for instance was one of these people who the public wasn't sure was a spy at the time. It was only after the opening of KGB records and the declassification of the VENONA program that people like Hiss clearly became agents of Soviet intelligence.

##The Rosenbergs:

Julius and Ethel Rosenberg were another duo who fell into the camp of uncertainty with their contemporaries. Exactly who was guilty of what is actually still controversial today (I've heard from some sources that Ethel's complicity with the espionage is still sorely debated -- it's not clear to some historians that the death penalty for treason was exactly justified) but what is clear to us now is that both were involved to some greater or lesser extent in the theft of nuclear secrets; again thanks mostly to the declassification of VENONA.

##General notes:

Since the collapse of the Soviet Union, the true volume of successes between the US and the USSR has become much more clear. The US as it turns out wasn't as successful at recruiting Soviet spies as the Soviets were at recruiting US spies, especially if you look at the raw numbers.

This doesn't mean that the US were complete failures in the intelligence game during the Cold War though, it just means that the US had a different set of skills.

US intelligence put a much heavier emphasis on technical intelligence collection methods developing some of the most successful aerial and satellite imagery collection platforms the world has ever seen. The U2, A12 and CORONA were all generations ahead of their time when they were being used, and still have a way of striking us with awe in their sheer engineering and design.

These are all general notes in response to the post, but reading the books and memoirs of those involved will give you a much more rich image of what we know only as a result of the fall of the soviet union and the declassification of a lot of what was being done back then.

The Korean War and Cuban intervention in Angola were always thought to be Soviet proxy wars. In fact, they were initiated by Kim and Castro who lobbied the Soviets for support. The tail wags the dog! Source: Armstrong, Charles. Tyranny of the Weak.

I got all excited by an archive question and wrote all the below… before revisiting the question and noticing that you were asking specifically about the Cold War. Oh well. The below largely concerns the impact on studies of Stalinism but you might still find it useful.

The opening of the archives has obviously has a significant impact on studies of the Soviet Union but not perhaps as much as you might think. It's very much deepened our understanding of the Soviet state and society during these decades but not, perhaps, revolutionised it.

To briefly recap, the political and economic debates of the early 1920s were relatively open. The leadership controversies, and the general cultural climate, produced a mass of published material for historians to draw on. By the end of that decade this had changed – the struggle against the Right Opposition largely happened behind closed doors and by 1930 published criticism of Stalin or the general line was unacceptable. This sharp change in atmosphere is apparent from the literature, even within individual books (as with Cohen's Bukharin), as non-archival sources dry up.

In this stifling atmosphere the best that Western historians could work from was those published sources (official releases, newspapers, self-criticism, etc) and accounts smuggled out of the country. These were cobbled together with educated guesses and logical leaps to draw broader conclusions. For example, Robert Conquest calculated, inaccurately as it turned out, remote camp populations based on ship schedules and their carrying capacity.

(Given the inherent problems with Soviet data, inventive interpretation is still often required today. Only now we have better base information to work off.)

Often, as in Lorimer's population figures, these were remarkably accurate. Often they weren't. But generally historians got pretty good at this. Gradual access to less sensitive archives (from the 1980s for Westerners, earlier for Soviet historians) helped and, while there were several bitter controversies, by the end of the Cold War there weren't many shocks left to be had. The opening of the archives showed that on the big questions at least some Western historians had gotten it largely right. For example, repression deaths tended towards the lower estimates and two generations of economic historians heaved a sigh of relief when it was demonstrated that the Soviets didn't (generally) falsify data.

So on the big questions the archives tended to either confirm what we knew or at least settle an argument by favouring one side or the other.

That said, there were important nuances to be added and plenty of these to be revised. Most notably, Stalin moved back to centre-stage as our the extent of his personal control over the state becomes apparent. The idea of a 'liberal opposition' in the Politburo and the Purges being triggered 'from below' (both popular in the 1980s) have been largely abandoned. So we now know more about the ruling elite ('Team Stalin' in Wheatcroft's memorable phrase). Similarly areas such as the mechanics of state repression or economic decision-making process have been impressively fleshed out. The archives have greatly deepened our understanding of how the Soviet state worked and how it interacted with its citizens.

But perhaps the greatest impact has been in opening up a whole new field of study. The mass of grassroots materials has enabled a 'linguistic turn' in new studies into the symbols and language of Stalinist power. There's been a host of detailed, and often conflicting, case studies that examine how Soviet authority was experienced by its citizens.

So the opening of the archives has substantially enriched our understanding of Stalin's USSR but has not, I'd suggest, transformed it. Attention has shifted away from the big controversies from the 1980s, towards a more detailed appraisal of how the Soviet state worked and how it was perceived/accepted by society.

Sources: There's a host of works referenced in passing above but Joseph Berliner has a good introductory chapter in Behind the Façade of Stalin's Command Economy on the impact of the archives. He's primarily concerned with economic and political history but it was around these that the big pre-archive controversies had ranged.

This is kind of a sub-question on this topic : How has the opening of the Soviet bloc archives in 1992 impacted the historiography of the Second World War?