Generals wonder what is happening "on the other side of the hill". Cold War historians wonder what is in the other side's archives.
During the Cold War, information was readily obtainable from open Western societies: information overload was the problem. Kremlinology and guess-work flourished. Espionage provided serious information for both sides.
East European and former Soviet archives, and some Chinese ones, are now being opened - gradually - to scholars. What are we learning?
The International Institute for Strategic Studies (IISS) in London recently organised a valuable discussion on "Re-thinking the Cold War", led by Prof Sir Michael Howard and Prof John Lewis Gaddis, the respected American "student of containment", whose latest book is We now Know: Re-thinking Cold War History.
Historians can now consider where they got it right or wrong. Gaddis cautiously spoke of an initial scholarly assessment rather than a definitive account. His finishing point was the Cuba missile crisis; documents are still emerging.
For him, the biggest surprise was the "role of ideology" in decision-making. Stalin's ruthlessness and realpolitik were known. But in his "world view" speech of February 9th, 1946, he predicted a third world war, not between the Soviet Union and the West, but between Britain and America; capitalists would be unable to cope with each other's contradictions.
The new information seems to show that this was not rhetoric, but a serious view. It helps to account for misjudgments after 1945, such as Stalin's failure to appreciate the co-operative processes which culminated in the Marshall Plan.
Despite good espionage information, Stalin still took the ideological view. The documents show his belief that the attractions of the system in a Communist East Germany would make all West Germany communist.
At the time, thousands of German industries were being dismantled and moved to Russia. An estimated two million German women were raped by Red Army soldiers. Chinese documents showed Mao in greater and longer deference to Stalin in the 1930s and 1940s than previously thought. When Stalin realised that the Marshall Plan was sealing off the spread of communism in Europe he shifted to Asia, where success seemed more likely.
Khruschev was concerned about a US invasion of Cuba, to crush communism in the hemisphere. Installing missiles was an ideological reaction.
Cuba then involved itself in Africa, without consulting Moscow. Ideological arguments were used to the Soviets: "You must support them or lose credit."
A Russian politburo member remarked that the Cubans were "realists" rather than "romantics" - people carried away by visions, ideas, opportunities. Stalin, Khruschev and especially Mao were all affected.
Sir Michael Howard said that both sides had peered over the brink during the Cuba crisis and pulled back. Things were never the same again.
Were the lengthy arms control discussions taken seriously by the Russians? Once multiple warheads (MIRVs) were invented control would have been extremely difficult.
In the 1970s America was undergoing the "tragic experience" of Vietnam and became, like the Soviet Union, cautious and conservative. For the first time, Germany took an initiative with Brandt's Ostpolitik. The State Department was not keen on this, but Kissinger used it.
The State Department saw the Conference on Security and Cooperation in Europe (CSCE) as a victory for the Soviets. But in the 1970s, when Vietnam, the Israel/Arab conflict and Watergate took up Americans' time, the CSCE agreement eased communications by human contacts with the satellites.
The many professors and students coming to the West saw the differences in living standards. By the end of the 1970s the only remaining genuine Marxists were in US and Western European universities.
The Soviet economy was sinking, the American view was apocalyptic. The Iranian revolution and the imprisonment of American diplomats strengthened the mood.
In the US, the Soviet invasion of Afghanistan was seen as a disaster for American policy. We saw it as a good sign; we knew the Afghans.
The US saw the strength of European opposition to cruise missiles (including Greenham Common) as the result of "Finlandisation". But we no longer saw the Soviet Union as the threat it had been.
And then, suddenly, it was all over.
Reagan's achievement lay in restoring US self-confidence, by a huge military investment, the implications of which remain.
Written pronouncements may not reflect politicians' actual thoughts, but as Prof Gaddis points out, historians are stuck with what has survived in documents. Significant things may not be written down. Finland was a good example. Stalin had good reason to expect Finnish resistance and an American reaction if he re-entered Finland after 1945. He said nothing about it.
Was the Cuba missile crisis more dangerous than was thought? The Soviet commanders obeyed orders not to use the missiles, but fired on American spy-planes against orders. Accidents are possible at lower levels.
Eric Hobsbawm, in Age of Extremes, is at odds with many of the ideas (should one say ideology?) presented above. Our world survived; let us be thankful.
Col E.D. Doyle is a former chief military observer for the United Nations in Sinai