Margaret MacMillan is the warden of St. Antony’s College, Oxford. She is a historian. She is the great granddaughter of David Lloyd George. And in her recent book, “Dangerous Games: The Uses and Abuses of History,” she quotes a recent Russian aphorism: “These days we live in a country with an unpredictable past.”

Now that President Obama and the Russians have sealed a nuclear treaty, and as the Americans’ former military and social rival moves to assume a conventional role among world powers, it is useful for Americans to remember what Russians never forget: Our history by and large is settled. The Russians’ history is still a matter of controversy, affecting their outlook, perspectives and conduct every day.

There are, to be sure, parts of American history that remain matters of contention. Just last month the Texas Board of Education dropped Thomas Jefferson from a list of major political thinkers, a gesture that will not be regarded kindly (or smartly) by history. And much of our contemporary debate is over whether the Constitution is a fixed or a living document, settled in its 18th-century form or affected by events, technological changes and social transformations of the past two centuries.

Consensus lacking

But basically Americans have a consensus about their history. The Russians do not.

Which is why it was startling not so long ago to find Russian President Dmitri A. Medvedev warning that the evils of Stalinism had been minimized in contemporary Russia, or to read of efforts by members of the Stalin family to prosecute newspaper commentators for slandering Stalin’s “honor and dignity.”

Stalin is a peculiarly complicated figure — a villain, to be sure, for prompting the death of tens of millions of people, but also an ally of the United States and Great Britain in the great struggle against another one of history’s monsters, Adolf Hitler, in World War II. He was a great builder (of a modern industrial state) and a great destroyer (of lives, culture and domestic tranquility).

So, too, was Soviet Russia a complicated place — a great manufacturing achievement, a great social disaster. But in the past several years, Vladimir Putin, now the prime minister of Russia, has expressed sorrow over Stalin’s victims — but also has described the destruction of the Soviet Union as “the greatest geopolitical catastrophe of the century.”

“They have blinders on if they want to feed that to the population,” says Vida Johnson, a Tufts University expert of Russian culture.

Past is always present

Yet the very fact that the collapse of communism is a subject of contemporary contention underlines how intimately interwoven are the past and the present in a country that might have too much of a past for its own good.

“The past is always present there,” says William C. Taubman, the Amherst College historian whose biography of Nikita Khrushchev won the Pulitzer Prize, “and always will be.”

Under both czar and commissar, that past includes famines, purges, pogroms, show trials, death camps, the oppression and repression of great artists and composers, censorship, the subjugation of ethnic minorities and other nations, and three continent-wide wars (Napoleonic, World War I and World War II) that left the country devastated. None of those things are prominent parts of the American landscape, though we, like the Russians, have fought a bloody civil war and have slaves and serfs in our backgrounds.

Troubled national memory

But there is a continuity in Russian history; many of the same features, ambitions and blind spots are prominent and recurring aspects of the country’s history. It is a history that the 20th-century Russian philosopher and theologian Georges Florovsky described as being “made up of interruptions, of paroxysms, of denials or enthusiasms, of disappointments, betrayals, ruptures.” All that contributes to a troubled national memory.

We don’t have a sanitized memory, at least not anymore. More than ever, slavery, for example, is regarded as a stain on America’s history and conscience. But since the mid-1950s, Americans of all races have confronted that stain, and increasingly are honest about it and try to learn from it.

Within the span of one lifetime the pioneers of the civil rights movement have gone from outsiders to insiders, from rebels to heroes. So it is no surprise that the newest biography of Barack Obama, David Remnick’s “The Bridge,” to be published Tuesday, opens at the Edmund Pettus Bridge, scene of a signature confrontation in the civil rights movement that in one generation has been transformed from a symbol of American acrimony to one of American accomplishment.

But Russians remain deeply conflicted about their history — a confusion that is understandable and perhaps worthy of our sympathy.

Ideological upheaval

This is less likely to be a character flaw than a characteristic of the sort of history Russians have endured. Russians have at least five traumas within living memory: rural collectivization, the frantic rush to industrial modernization, Stalin’s purges, World War II, the collapse of the Soviet Union. No other country in the world, with the possible exception of China, has had to cope with so much death, destruction and ideological upheaval.

It adds up to an unmanageable burden — what Tim McDaniel, a sociologist at the University of California at San Diego, calls “the tragedies of social breakdown, revolution and civil war that have afflicted modern Russia.”

As a result, McDaniel argues in “The Agony of the Russian Idea,” his 1996 examination of Russian history and culture, “the past is regarded not as the foundation of organic growth, but as the source of error that must be completely destroyed.”

Just a month ago, former Soviet leader Mikhail Gorbachev wrote a piece for The New York Times op-ed page in which he argued for continued modernization of Russia and increased democratization of the political system. “What’s holding Russia back is fear,” he wrote. “Among both the people and the authorities, there is concern that a new round of modernization might lead to instability and even chaos. In politics, fear is a bad guide; we must overcome it.”

The message here is clear. Russia must overcome its fear. But first it must come to grips with its history.