From the Vietnam War until the end of the Cold War, it was almost axiomatic that liberals would oppose every use of American military power. Defecting from that position was what qualified a former liberal as a neoconservative. But in the last 20 years, as the post-Holocaust promise “never again” was betrayed in Rwanda, Bosnia, and Darfur, parts of the left began to reconsider the virtues of force. In certain desperate crises, it now seemed, war might be the most humane response, the only way for Americans to put a stop to massacre and genocide. The era of “humanitarian intervention” was born, and the old constellations of the foreign-policy debate were realigned. The far left, always mistrustful of American power, and the far right, true to its isolationist traditions, joined in opposing the NATO bombing of Serbia during the Kosovo war. The Iraq war — initially at least — brought together realists concerned about weapons of mass destruction with idealists who wanted to overthrow Saddam Hussein’s murderous regime.

Today, however, the idea of humanitarian war has fallen on hard times. Burned in Iraq, America is now twice shy about projecting its military power, even in the most dire emergencies: Just look at the failure of the Darfur campaign to gain any traction among a war-weary American public. In “Freedom’s Battle” (Knopf, 528 pages, $35), Gary Bass, a professor at Princeton who is the author of a highly regarded book on war-crimes trials, sets out to rehabilitate the idea of humanitarian intervention, by providing it with a history that stretches back much further than 1989. Mr. Bass examines three episodes during the 19th century when Britain and France considered intervening in the affairs of the Ottoman Empire, in order to punish or prevent massacres of Turkey’s minority Christians. In Greece in the 1820s, Syria in 1860, and Bulgaria in 1876, Mr. Bass argues, we can find examples of the kind of disinterested intervention that American liberals called for in Rwanda and Bosnia.

By establishing this lineage, Mr. Bass hopes to steal a march on the foreign-policy “realists,” such as Henry Kissinger, who look to the 19th century as a golden age of realpolitik and balance-of-power diplomacy. On the contrary, Mr. Bass writes, “All of the major themes of today’s heated debates about humanitarian intervention … were voiced loud and clear throughout the nineteenth century. In their elegant cursive, in dispatches ornamentally sealed with red wax and delivered in safe boxes, the diplomats of a century and three-quarters ago were negotiating many of the same questions that Bill Clinton faced in Bosnia and Rwanda and that George W. Bush faced in Congo and Darfur.” It follows that if even George Canning and Lord Palmerston, those famously hardheaded statesmen, sometimes sent British troops across Europe to stop a massacre, then their 21st-century counterparts have every right to do the same.

While they may not play much of a role in current foreign-policy debates, the episodes that Mr. Bass writes about are hardly unknown. You cannot read much English Romantic poetry, for instance, without running into the Greek War of Independence, so large a part did it play in the imagination of English radicals in the 1820s. To Byron and Shelley, Greeks fighting to throw off the Ottoman yoke were taking part in the same struggle between liberty and tyranny that inspired the French Revolution. It was especially easy to cherish the Greeks because of the special role of ancient Greek language and literature in an Englishman’s education. Shelley spoke for his generation when he imagined 19th-century Greece as a second coming of Athens, where “A loftier Argo cleaves the main, / Fraught with a later prize; / Another Orpheus sings again, / And loves, and weeps, and dies.”

Byron, who actually enlisted in the Greek army, found that the reality was quite different. “I cannot say much for those [Greeks] I have seen here,” he complained. The rebellion was hampered by factionalism, corruption, and incompetence, and the spirit of Pericles was nowhere to be found. The poet himself died of fever before he did any actual fighting; but even this ambiguous martyrdom, Mr. Bass shows, was a propaganda coup for the Greek cause.

Even more important in galvanizing English opinion, however, was news of Turkish atrocities such as the massacre on the island of Scio, where in April 1822 the Turks killed some 25,000 Greeks. Instantly, as Mr. Bass writes, Scio “became as notorious as Guernica or Srebrenica — no longer just the name of a place, but a synonym for massacre of the worst kind.” Just as Picasso memorialized the German bombing of Guernica, so Delarcroix painted “Scenes of the Massacre at Scio,” which Mr. Bass describes as a “horrifically vivid painting” featuring “a woman being raped by a Turk still wearing his fez.”

The reaction of the English public to such atrocities put pressure on the government to intervene in Greece, much against the wishes of Tory “realists” such as Castlereagh and Wellington. Things came to a head when a rumor reached England that the Ottoman general Ibrahim Pasha was planning to “remove the whole Greek population, carrying them off into slavery in Egypt” — in other words, to commit what we would now call genocide. Rather than permit such a crime, Britain, France, and Russia joined their naval forces to attack Ibrahim’s fleet off the Greek coast. The battle of Navarino, in which the entire Turkish fleet was sunk, marked the effective end of the Greek War of Independence.

Seen in a certain light, Navarino does look like an early example of humanitarian intervention. The same can be said of France’s involvement in Syria in 1860, when Napoleon III sent 6,000 troops to put an end to Druze massacres of Maronite Christians. And humanitarian motives were certainly at work in the bruising British debates of the 1870s, when Gladstone and the Liberals chastised Disraeli and the Conservatives for failing to take action to stop Turkish massacres of Bulgarian Christians. In each case, advanced Western opinion condemned distant atrocities, out of what appeared to be simple altruism.

Yet if you adjust your perspective just slightly, the story that Mr. Bass has to tell in “Freedom’s Battle” starts to look very different. Mr. Bass never really takes account of the obvious fact that each of his three episodes has to do with Anglo-French intervention in the Ottoman Empire. In the period Mr. Bass is writing about, the Eastern Question — the question of how to manage the decline of Ottoman power — was the central problem in European diplomacy. All the great powers were jockeying for position in the Near East, especially Britain, whose long-standing policy was to prop up Turkey as a bar against Russian expansion. One of the ways the European powers gained a say in Turkish affairs was to claim the right to protect the sultan’s Christian subjects: France was the special guardian of the Maronites, Russia of the Orthodox; at times, Britain flirted with a special relationship with the Jews of Palestine.

In this context, Britain’s solicitude for Greeks and Bulgarians cannot be considered simply altruistic. There were moral passions involved, certainly, but they went hand in hand with a larger geopolitical and ideological effort to supplant the Ottoman Empire. When it was useful, British humanity could be contrasted with Turkish inhumanity as part of this effort. But as Mr. Bass occasionally notes, “humanity” was not considered to be binding on British troops in India, where the 1857 Sepoy Mutiny was put down with a savagery Ibrahim Pasha would have admired. Similarly, Napoleon III conspicuously restrained his soldiers’ behavior in Syria, hoping to impress the world with his fair-mindedness; but he had no such compunctions when it came to invading Vietnam.

Mr. Bass insists that, all the same, it is possible to distinguish humanitarian intervention from simple imperialism. Yet he skips much too quickly over what is, in fact, the central lesson of his own book. “The British and the French in this period,” Mr. Bass admits, “were convinced that they were heralds of superior culture and enlightened government. In that sense, they did have a kind of imperialistic consciousness that was part of the argument for rescuing Greeks, Syrians, and Bulgarians.” It was this conviction of superiority — based not just on “enlightenment,” but on Christianity, technological sophistication, and military power — that enabled the British Empire to do so much harm and good in the world. For America to act as a benign hegemon, as Mr. Bass desires, it might mean that we have to imitate the British Empire in more than just its humanitarian moments. Whether that is possible, and worth the price, is the central foreign-policy question of our time, but “Freedom’s Battle” does not answer it quite as clearly as Mr. Bass thinks.

akirsch@nysun.com