"We now know" the truth about the Cold War, declared historian John Lewis Gaddis of Yale University in his 1997 book of that title. In fact, there is still a great deal we do not know, and much work remains to be done on many specific incidents and aspects of Cold War history. Lorenz M. Luthi, one of Gaddis' former students at Yale and currently an assistant professor of international history at McGill University in Montreal, has written an exhaustive and important study of one of the most critical events of that history, the so-called Sino-Soviet split of the late 1950s and early 1960s. In February 1950, China and the Soviet Union signed a "Friendship Treaty" that seemed to signal a long-term and (for the West) ominous alliance. Ten years later, that alliance was in tatters, and by the end of the 1960s the two sides were shooting at each other across parts of their long border. Despite the importance of the Sino-Soviet conflict, little about it could be assessed by primary research because of the closed nature of both societies -- until now.

Almost 20 years after the fall of the Berlin Wall, scholarly access to the archives of former communist states continues to transform our understanding of the Cold War. Yet few Western scholars have had the training and the patience to do the sort of multilingual, multinational, multiarchival work necessary for solid research in this area. Luthi not only has done thorough research in the Russian- and Chinese-language documents, but also has explored the archives in German, Polish, Czech, Hungarian, Italian and French. The result is an astonishingly well-documented, densely detailed history of the causes and development of the Sino-Soviet conflict from virtually every relevant perspective.

Of course, the Sino-Soviet split was a major concern of Western scholars at the time (although many were slow to recognize its emergence under the facade of socialist "friendship"), and Luthi has to deal with the contemporary political science literature on the subject, as well as the history of the rupture itself. He does so deftly and succinctly in the book's introduction, in which he criticizes some of the Cold War-era explanations for the split, which focused on competing national interests, the Sino-U.S.-Soviet strategic triangle and the primacy of domestic politics. For his part, Luthi emphasizes ideology as the key motivating factor in the Sino-Soviet conflict -- that is, differences between Moscow and Beijing over the "correct" interpretation and practice of communism. Each side accused the other of apostasy from true communism: For the Soviet Union, China was dangerously "leftist" and "adventurist"; for China, the Soviet Union was too conservative, or "revisionist," both internally and in its dealings with U.S. imperialism.

However, it is often difficult to separate "pure" ideology (whatever that may mean) from other motivations. Luthi says at several points that ideology "had both instrumental and genuine characteristics," but it is not always clear what is instrumental and what is genuine. Sino-Soviet relations were best when the Soviet Union was ruled by Josef Stalin, arguably the most cynical leader in Soviet history, but one can dispute whether this was because ideology was downplayed or because China was relatively weak and dependent at the time. Nikita Khrushchev, who saw himself as a more genuine communist than Stalin, later managed to alienate not only Mao Zedong but also many other communist leaders. Perhaps communists get along best when ideology is merely instrumental. Narrowly focused on the late 1950s and 1960s, Luthi doesn't much explore the implications of his interpretation for Sino-Soviet relations in earlier and later periods.

Itar-Tass A tribute to the builders of communism marks the tense border between the U.S.S.R. and China in 1969.

Luthi attributes the Sino-Soviet split to three main points of conflict between the two countries: the communist economic model, de-Stalinization and policy toward the West. It may be going too far to say, as Luthi suggests, that these three conflicts were primarily ideological. All had a great deal to do with domestic politics, strategic interests and each country's respective position as a leader of world communism. But certainly these conflicts were expressed in ideological terms, and one thing post-Cold War scholarship has confirmed is that in many cases -- especially in Third World communist states and movements, such as in China and Cuba -- ideology was a more genuine motivation than many cynical Western observers realized at the time. The Chinese side was far more active than the Soviet one in pursuing ideological conflict, and questioned Moscow's communist bona fides at every turn, from the dispute over Taiwan, to detente with the West, to modernizing the economy. There is no doubt that the leaders of the People's Republic of China wished to prove their country to be a more genuine communist state than their erstwhile benefactor, the Soviet Union. The result, for China, was famine, international isolation and the chaos of the Cultural Revolution in the late 1960s.

Neither the Soviet Union nor China fares well in Luthi's analysis, but China looks worse. Throughout the book, there is a recurrent dynamic of Chinese provocations and Soviet blunders. Much of this can be traced to the personalities of Mao and Khrushchev, which might be reduced to impulsiveness and arrogance, respectively. Indeed, Mao appears extraordinarily foolhardy -- at times almost out of touch with reality. His quixotic domestic policies and self-isolating attacks on virtually all "fraternal" states and parties, not to mention his provocative actions against the United States, may have given Mao the ideological upper hand but were disastrous for his country. Khrushchev, more cautious and accommodating to both his enemies and his allies, ended up fighting a Cold War against both China and the United States, and Khrushchev's successors found themselves facing a quasi-alliance between the United States and China. The three-way balance between these countries may not have mattered much to the Soviet Union and China in the 1960s, but the United States took it seriously enough to align itself with the much more radical of the two communist giants in the 1970s. Thus, the strategic triangle was a result, not a cause, of the Sino-Soviet split.

The bulk of "The Sino-Soviet Split" is a richly detailed, mostly chronological story of the evolution of Sino-Soviet relations from fraternal alliance to the brink of armed conflict, ending with the collapse of their military alliance during the Vietnam War. The Vietnam case, however, suggests that China and the Soviet Union were not always in conflict in their foreign relations, even when mutual recrimination was at its peak. After all, Moscow and Beijing both continued to give military aid to North Vietnam throughout its war with South Vietnam and the Americans. Common interests could at times trump ideological differences.

Sometimes Luthi appears too uncritical of sources, especially secondary sources, such as Li Zhisui's controversial "The Private Life of Chairman Mao." Unsupported by other types of evidence, secondhand memoirs such as Li's can cross the line into gossip. But on the whole, Luthi's use of multiple, cross-referenced sources is exemplary, if still limited by uneven access. Whereas access to Soviet sources, and even more to those of former communist states in Eastern Europe, is quite extensive, access to Chinese sources remains selective and limited. Unlike Russia, China still has a ruling Communist Party that can vet documents available to scholars, especially foreign scholars. Paradoxically, this may partly explain why China looks worse in Luthi's account, as he has to fill in the document gap on the Chinese side with anecdotes, memoirs and third-party accounts.

"The Sino-Soviet Split" is a major achievement in Cold War history and the standard against which future scholarship on this subject likely will be judged for many years to come. Nevertheless, to suggest that any study is the "final word" on any topic is profoundly ahistorical. As Mao himself allegedly said, when asked about his evaluation of the historical impact of the French Revolution: It's too early to tell.

Charles K. Armstrong is an associate professor of history at Columbia University and the author of "The North Korean Revolution, 1945-1950." He is currently writing a book on North Korean foreign policy in the Cold War era.