When policy makers disparage Kissinger in private, they tend to do so in a manner that reveals how much they measure themselves against him. The former secretary of state turns 90 this month. To mark his legacy, we need to begin in the 19th century.

In August of 1822, Britain’s radical intelligentsia openly rejoiced upon hearing the news of Robert Stewart’s suicide. Lord Byron, the Romantic poet and heroic adventurer, described Stewart, better known as Viscount Castlereagh, as a “cold-blooded, … placid miscreant.” Castlereagh, the British foreign secretary from 1812 to 1822, had helped organize the military coalition that defeated Napoleon and afterward helped negotiate a peace settlement that kept Europe free of large-scale violence for decades. But because the settlement restored the Bourbon dynasty in France, while providing the forces of Liberalism little reward for their efforts, Castlereagh’s accomplishment lacked any idealistic element, without which the radicals could not be mollified. Of course, this very lack of idealism, by safeguarding the aristocratic order, provided various sovereigns with the only point on which they could unite against Napoleon and establish a continent-wide peace—a peace, it should be noted, that helped Britain emerge as the dominant world power before the close of the 19th century.

One person who did not rejoice at Castlereagh’s death was Henry John Temple, the future British foreign secretary, better known as Lord Palmerston. “There could not have been a greater loss to the Government,” Palmerston declared, “and few greater to the country.” Palmerston himself would soon join the battle against the U.K.’s radical intellectuals, who in the early 1820s demanded that Britain go to war to help democracy take root in Spain, even though no vital British interest had been threatened—and even though this same intellectual class had at times shown only limited enthusiasm for the war against Napoleon, during which Britain’s very survival seemed at stake.

In a career spanning more than two decades in the Foreign Office, Palmerston was fated on occasion to be just as hated as Castlereagh. Like Castlereagh, Palmerston had only one immutable principle in foreign policy: British self-interest, synonymous with the preservation of the worldwide balance of power. But Palmerston also had clear liberal instincts. Because Britain’s was a constitutional government, he knew that the country’s self-interest lay in promoting constitutional governments abroad. He showed sympathy for the 1848 revolutions on the Continent, and consequently was beloved by the liberals. Still, Palmerston understood that his liberal internationalism, if one could call it that, was only a general principle—a principle that, given the variety of situations around the world, required constant bending. Thus, Palmerston encouraged liberalism in Germany in the 1830s but thwarted it there in the 1840s. He supported constitutionalism in Portugal, but opposed it in Serbia and Mexico. He supported any tribal chieftain who extended British India’s sphere of influence northwest into Afghanistan, toward Russia, and opposed any who extended Russia’s sphere of influence southeast, toward India—even as he cooperated with Russia in Persia.