French President Nicolas Sarkozy posed the essential question a few weeks ago when he asked, "Does Europe want peace, or does it want to be left in peace?" Well, as Groucho Marx said, when asked if he was a man or a mouse: "Put a piece of cheese on the floor, and you'll find out."

Of course Europeans want to be left in peace. They experienced enough turmoil in the 20th century to last a millennium: two world wars that devastated the continent and took tens of millions of lives; the Holocaust, which still inspires deep guilt, and not only in Germany; the rampant inflations and depressions of the 1920s and 1930s; the wild political swings; the Cold War that divided the continent. Just beneath the skin, all of Europe remains deeply scarred.

So how surprising is it that what Europeans yearn for in their self-contained world is stability and predictability, a little peace and quiet? That revolutionary innovation in geopolitics, the European Union, arose from a deep conservatism — a fear of the turmoil that can be caused by unconstrained ambitions. The E.U.'s economic strictures, which now act as a barrier to Keynesian deficit spending, were put there by the Germans, for whom memories of inflation, not depression, are the great nightmare. The Germans and French prefer welfare payments to government stimulus spending, part of the system of social safety nets on which their citizens have grown so comfortably dependent. Better to regulate more tightly the international capitalists who can cause havoc with their inventiveness. Better to be less rich than less secure.

There have been brief moments of European global ambition. In the late 1990s, Tony Blair and Jacques Chirac joined hands to promote a more muscular European military. They were troubled by the vast military superiority, and accompanying arrogance, of the Americans during the Bosnian and Kosovo conflicts and were determined to make Europe an independent global player. A few years later, the great thinker and strategist Robert Cooper envisioned E.U. enlargement as postmodern Europe's contribution to global security, the "voluntary liberal empire" that would expand the zone of peace, liberalism and security to Turkey, the Balkans, Ukraine and what Europeans called the continent's "new neighborhood."

But Europe has largely recoiled from those fleeting ambitions. The E.U. army remains as distant a prospect as it was a decade ago. The eastward enlargement of 2004 produced indigestion and is regretted by many Western Europeans. Fear of Russia limits talk of admitting Ukraine, much less Georgia. Fear of Islamicization has killed any hope of admitting Turkey.

It is into this Europe that President Obama has flown, with what Europeans regard as some radical and frightening plans for the economy; with a new strategy for Afghanistan and Pakistan that is far more aggressive, militaristic and success-oriented than they would prefer; with ideas about Iran that are welcome (the promise to talk) but also unnerving (the threat to impose more sanctions). As one savvy French journalist told me, "We have all been surprised. He is so ... American!"

Americans are creators of turmoil. Europeans see them the way the ancient Greeks saw the Athenians, as "incapable of either living a quiet life themselves or of allowing anyone else to do so." As the scholar Stephen Sestanovich pointed out in a brilliant essay on "American Maximalism," Democratic and Republican administrations alike over the past half-century have favored "large, even risky" transformative strategies, whether confronting the Soviet Union, unifying Germany, fighting in the Balkans or solving global economic crises, and have abjured the safer, incremental approaches that Europeans prefer.

Europeans love Obama, but European leaders have been fretting ever since his election. George W. Bush did the Europeans a huge favor by giving them the best excuse for inaction in trans-Atlantic history. Now comes Obama, so much more compelling and yet, still, American.

One wonders whether Obama officials quite see the enduring gap between Europe and the U.S., or whether they have convinced themselves it was merely a creation of Bush and will now vanish. This was the view put forth by a senior administration official in Brussels recently. But Europeans, and presumably seasoned veterans such as Richard Holbrooke, know better. The question is whether the Obama administration, like some previous U.S. administrations, can get Europe to do what Americans believe needs doing. Or perhaps, in the interest of comity, it will tacitly accept that most Europeans don't want to send more troops to Afghanistan, spend more on defense or on economic stimuli, impose tougher economic sanctions on Iran, or stand firm against Russia's many demands. Instead of challenging them to do more, the administration may politely move on without them: the soft unilateralism of low expectations.

Robert Kagan is a senior associate at the Carnegie Endowment for International Peace. He wrote this commentary for the Washington Post.