Henry Kissinger began contributing to America’s national security during World War II. After fleeing Nazi Germany in August 1938 at the age of 15, attending George Washington High School and City College in New York, Kissinger was drafted into the U.S. Army and selected for the Army Specialized Training Program, which, as Niall Ferguson noted in Kissinger 1923–1968: The Idealist, “sent academically able soldiers to colleges all over the country” — in Army Private Kissinger’s case, to Clemson and Lafayette College. He trained for war with the 84th Division in Louisiana, where he met Fritz Kraemer, who later remembered that Kissinger was “musically attuned to history.” He would remain so the rest of his long life. It was history that informed Kissinger’s realism.

The 84th Division, after a stay in England, landed on Omaha Beach in November 1944. The 84th joined other American divisions in attacking the Siegfried Line. After the scare of the Battle of the Bulge, Kissinger crossed the Roer River as part of Operation Grenade led by Gen. William Hood Simpson’s Ninth Army. After crossing the Rhine, Kissinger was selected to command a counterintelligence unit and earned a Bronze Star. With Germany’s defeat, U.S. army counterintelligence focused on the communist threat to Eastern and Central Europe — the Cold War, which would shape Kissinger’s career, had begun.

Kissinger taught a course on Eastern Europe and the threat of communism at the European Theater Intelligence School in Oberammergau, Germany. His academic career continued in the United States at Harvard, where he wrote a senior thesis titled “The Meaning of History” that focused on the writings and thought of Oswald Spengler, Arnold Toynbee, and Immanuel Kant. The war and great theorists of history further shaped Kissinger’s realism. Still an army reservist, Kissinger was sent abroad to report on American occupation policies in Japan and Germany. He also began an international seminar at Harvard that invited some of the West’s leading foreign policy thinkers to lecture students and contribute to a quarterly journal called Confluence. Policymakers in Washington, including Nelson Rockefeller, soon took notice.

As the Cold War turned hot in Korea, and as the superpowers engaged in a nuclear arms race, Kissinger wrote two works that counseled prudence and realism as antidotes to the danger of nuclear apocalypse. A World Restored: Metternich, Castlereagh and the Problems of Peace, 1812–22 analyzed and praised the diplomats at the Congress of Vienna who organized a Concert of Europe to maintain peace and equilibrium in the wake of the Napoleonic world wars. It was a refutation of Wilsonian utopianism in foreign policy — a subject Kissinger returned to 40 years later in his book Diplomacy (1994). What Kissinger prized most was stability and order, which, as he explained, do “not make conflicts impossible, but … limits their scope.” Metternich and Castlereagh, he wrote, “rescued stability from seeming chaos” in Europe. Those statesmen “reconcile[d] what is considered just with what is considered possible.” They both had the ability “to recognize the real relationship of forces and to make this knowledge serve [their] ends.” They eschewed “undisciplined sentimentality” while “coolly and unemotionally” forging an equilibrium. The message of A World Restored to U.S. policymakers was to step back from Armageddon and search for a tolerable global equilibrium.

In Kissinger’s next work, he applied those notions to the nuclear arms race. Nuclear Weapons and Foreign Policy was written under the auspices of the Council on Foreign Relations. It criticized the Eisenhower administration’s declared policy of “massive retaliation” and argued that even nuclear war could be limited and serve political ends. It foreshadowed Herman Kahn’s On Thermonuclear War and influenced the foreign policy advisers of then-Sen. John F. Kennedy. Nuclear Weapons and Foreign Policy was, in a sense, the intellectual foundation of the Kennedy administration’s “flexible response.” Kissinger understood that a pledge to commit mutual suicide was not very credible. Effective deterrence required posturing for a limited nuclear war and greater reliance on conventional forces. Ironically, it was Defense Secretary Robert McNamara of the Kennedy and Johnson administrations who championed mutual assured destruction (MAD) and willingly allowed the Soviet Union to achieve nuclear parity with the United States — a doctrine that Kissinger would later criticize in the late 1970s. (READ MORE: Russia’s Top Officials React to Henry Kissinger’s Death)

Kissinger did consulting work for both the Kennedy and Johnson administrations. But he left his mark on American national security policy in the Nixon and Ford administrations, where he served as national security adviser and secretary of state (for a time, in both posts). Kissinger, with Nixon’s blessing and encouragement, brought realism to the center stage of American foreign policy. It was as if John Quincy Adams was back at the State Department. America had no permanent friends and no permanent enemies, only permanent interests, to paraphrase Lord Palmerston. Nixon and Kissinger toned down the ideological rivalry with Moscow and Communist China. Their triangular diplomacy ensured that Eurasia would remain politically divided. Their Middle East policy lessened Soviet influence while relying on allies in the region (Israel, the Shah of Iran, the Saudis) to advance U.S. interests. They set in place policies — imperfect though they were — that ended U.S. involvement in the Vietnam War, which was fracturing the republic. Stability, equilibrium, and prudence were the watchwords of U.S. foreign policy. The accomplishments of the Nixon–Ford foreign policies, as Kissinger argued in the third volume of his memoirs, set the geopolitical stage for the end of the Cold War.

Watergate doomed Indochina. The Carter administration’s amateurish foreign policy encouraged a Soviet geopolitical offensive in Africa, Latin America, and the Caribbean. Out of power, Kissinger continued his contribution to American national security policy by becoming a public critic of Carter’s disastrous foreign policy that abandoned allies in Iran and Nicaragua, cut back on planned strategic weapons programs, and raised “human rights” to an unprecedented place in U.S. foreign policy. But Kissinger’s greatest foreign policy triumph — the opening to China in the context of triangular diplomacy — remained in place. As long as China and the Soviet Union remained geopolitically apart, Eurasian equilibrium would bolster American security.

During the Reagan administration, Kissinger headed up a commission on conflicts in Central America that publicized the communist threat on our geographical doorstep. He was consulted by the Reagan and George H.W. Bush administrations as the Soviet Union unraveled. But like George Kennan, Kissinger, while welcoming the Soviet collapse, recognized that in international relations, victories are seldom permanent.

In the euphoria of the collapse of the Soviet Union, Kissinger warned his countrymen that there was no such thing as an end to international rivalry and conflict. Pundits and some policymakers declared an “end to history,” celebrated America’s “unipolar moment,” and sought to reclaim a “peace dividend.” It was in this context that Kissinger wrote his most important book, Diplomacy. It was the first of several post–Cold War books by Kissinger that used historical examples to return to his themes of balance, equilibrium, prudence, and realism. Kissinger’s “heroes” in Diplomacy are Richelieu, Metternich, Palmerston, Bismarck, Disraeli, Theodore Roosevelt, and Nixon. Diplomacy ranks with the best of classical geopolitical works, such as Halford Mackinder’s Democratic Ideals and Reality, Nicholas Spykman’s America’s Strategy in World Politics, Hajo Holborn’s The Political Collapse of Europe, and Alfred Thayer Mahan’s The Problem of Asia. Kissinger recognized the Wilsonian strain in American foreign policy and the domestic political limitations it puts on the exercise of American power and diplomacy. But he showed that Wilsonian crusades often lead to foreign policy disasters.

In his 99th year, Kissinger wrote Leadership: Six Studies in World Strategy. Here, again, Kissinger used history and history’s policymakers to support his realist approach to international politics. In this book, his heroes are Germany’s Konrad Adenauer, France’s Charles de Gaulle, Egypt’s Anwar Sadat, Britain’s Margaret Thatcher, Singapore’s Lee Kuan Yew, and Nixon again. Like his earlier heroes Metternich and Castlereagh, Kissinger’s subjects in this book eschewed ideology in favor of pragmatic conservatism. They all “fit means to ends and purpose to circumstance.”

For Kissinger, history and personal experience (Nazi rule in the land of his birth, combat in World War II) forged in him what Robert Kaplan calls a “tragic mind.” Kissinger understood that tragedy weaves its way throughout human history in the form of natural disasters, wars, plagues, terrorism, ideological fanaticism, autocratic brutality, fear, and accidents. He, of course, was not a perfect statesman — realists know that human perfectibility is a chimera. But in his military service, his academic writing, his consulting work, and his policymaking, Henry Kissinger dutifully, and at times brilliantly, served his adopted country for eight decades.

R.I.P.