"America's mission in Iraq," the president proclaimed in his speech at Fort Bragg on Tuesday, "is . . . a free, representative government that is an ally . . . and a beacon of hope in a part of the world that is desperate for reform." And it should be a nation, he continued, "that can govern itself, sustain itself and defend itself."

A tall order. Contrary to the rosy picture of our past so prevalent in Washington today, this country possesses a rich and often troubled history of intervention and nation building, and even empire. We succeeded in building democracy at home but largely failed in planting it abroad, which ought to make all of us, the president included, wary of so vague a goal in Iraq, and exceedingly careful in crafting a strategy to set that country on the road to stability and independence.

From the very beginning, we were nation builders. At the same time as they created a republic, the Founders themselves spoke enthusiastically and confidently about a rising American empire. 19th-century successors expanded over the continent (our "Manifest Destiny"), conquering and then ultimately forcing the Indians onto reservations. End-of-century colonization of foreign lands in the Caribbean and western Pacific was followed by 20th-century occupations in Europe and Asia. And our own generation has overthrown governments in Panama and Haiti, sent troops into Somalia, Bosnia, Kosovo and elsewhere, and now has embarked on nation building in Afghanistan and Iraq.

It is clear from looking back over these many attempts that when the president claimed on Tuesday that we have "made progress, but we have a lot of -- a lot more work to do," he spoke a larger truth than even he perhaps realizes.

We seem to have forgotten just how difficult our own struggle at home for democracy, freedom, social justice and national security has been. Our liberties grew over time, in fits and starts, with periods of violence -- race riots, labor strife, domestic bombings, veterans' protests, the upheavals of the 1960s. It took nearly a century and a catastrophic civil war to abolish slavery. It took another 60 years to enfranchise women. Sometimes liberty regressed, for example in time of war -- a possibility expressed frequently today as Congress debates renewing the Patriot Act and the courts struggle with definitions of freedom of the press.

Abroad, the American experience has been marked by decidedly less success. Over the course of our history, we have occupied defeated enemies (Mexico in the 1840s, Japan in the late 1940s and Germany -- twice -- after the two World Wars), sent troops into countries where our interests were threatened, assisted nations under attack, and overthrown regimes that threatened us in some way. The few times that the United States has attempted to defeat insurgencies or build viable democratic regimes, it has sometimes met with temporary success but ultimately, almost always failed.

Between 1898 and the early 1930s, American soldiers and Marines intervened in or occupied countries in the Caribbean and Central America almost 20 different times to protect U.S. economic interests or to develop the countries or simply to suppress revolts and provide order. Democracy was rarely if ever the result. Interventions during the Cold War -- whether overt or covert -- usually propped up unsavory undemocratic governments in an effort to combat communism. And while some interventions -- Nicaragua and Panama in the 1980s -- fostered democracy, others, like Chile, had the opposite result.

While nation building in Asia has been more successful, it was marked by notable failures. In the Philippines, after suppressing the insurrection against American rule between 1899 and 1903, the United States maintained permanent garrisons to support a colonial administration, didn't relinquish control until the mid-1940s, had assisted in defeating a communist insurgency in the 1950s, then watched the country slip back into dictatorship before democracy took hold in the late 1980s. Japan was perhaps the most dramatic success, but South Korea suffered Syngman Rhee's autocracy and then decades of military authoritarianism before democracy emerged. The United States never succeeded in liberalizing Ngo Dinh Diem's government in South Vietnam before acquiescing in military rule and then North Vietnamese victory in 1975.

Since the Cold War, the record has been ambiguous. Progress in Bosnia has been painfully slow, 10 years after American troops arrived intending to stay but a year, and few would count that country -- or its Kosovo neighbor -- as a free, democratic regime able to defend itself. Twice U.S. troops have been sent to Haiti without even stabilizing that troubled nation, much less solidifying democracy. None of this bodes well for the continuing conflicts in Afghanistan and Iraq.

Each example, of course, stands alone -- the product of place and time, the individual experience of a country and its population, and the actions undertaken by the governments and groups involved. But the history suggests that democracy, freedom and liberty take root slowly and face formidable obstacles even in a country such as ours that inherited a reverence for law, and after 1815 grew for over a century without significant foreign threats to national security.

Few would suggest that today, with American and others' experience to draw upon, democratization needs to be as slow as it was in the United States and Europe. Indeed democratization has advanced dramatically in many places in the last 25 years. But in societies less blessed with the advantages of the United States and other western democracies, the challenges are immense and sometimes the push for democracy can actually slow or even reverse freedom and liberty.

In a country where there is a history of colonial subjugation and autocratic rule, clan or ethnic rivalries and religious hatreds, discrimination against minorities and women, and underdeveloped or dependent economies, the obstacles are all the greater. The absence of such norms as the respect for equality, religious freedom, civil liberty, civilian control of the military and political compromise -- even when no foreign or domestic foes are threatening force -- indicates that the United States will have to make some very difficult choices in Iraq during the next few months.

Withdrawal while the insurgency rages even at a slower tempo will invite chaos and civil war, and clearly a defeat of the president's intentions. Staying for many years, with a large American military presence, is likely not only to weaken the Iraqi government but to stimulate jihadi recruitment and attacks, undermining the larger war on terrorism.

The moderate course in between, which the administration is pursuing, possesses dangers of its own. The fighting must be turned over largely to the Iraqis and quickly -- in a year or two. Explicit milestones and a reduced American footprint will have many advantages: revealing our strategy and marking its progress in order to maintain American patience and gain international support; diluting enemy propaganda about our motives; and removing a major impulse behind the insurgency.

More important will be the progress of Baghdad's government, on which all else rests. Here history suggests that we will have to assess its character with a more realistic standard of what's possible. "The mission" must be defined with greater precision than the president offered last Tuesday if the American people are to accept continuing expenditures of blood and money. Sooner or later we will need a realistic rendering of what "success" involves. Squishy generalities won't suffice; the public has a keen nose for fakery and fraud. The president knows "that Americans want our troops to come home as quickly as possible." If, as he says, "So do I," he may have to accept a less robust definition of a free and democratic government in Iraq -- and its analogue elsewhere in the Middle East -- than he asserted this past week. If he won't, then the American people will have to force an outcome more in keeping with historical reality.

Richard Kohn, a military historian and former chief of history for the U.S. Air Force, chairs the Curriculum in Peace, War, and Defense at the University of North Carolina at Chapel Hill.

Fits and starts: After suppressing an insurrection against American rule in the late 1890s, the United States didn't give up control of the Philippines until the mid-1940s. Democracy only took hold in the late 1980s, after a lengthy dictatorship backed by successive U.S. presidents.