Kenneth N. Waltz, a widely admired scholar of international relations who was best known to the broader public for his theory that, as far as nuclear weapons are concerned, “more may be better,” died May 12 at a hospital in New York City. He was 88.

He had pneumonia, said Mira Rapp-Hooper, his research assistant at Columbia University. Dr. Waltz had taught for more than two decades at the University of California at Berkeley before joining the Columbia faculty in the 1990s.

Dr. Waltz ranked among the top five most influential scholars of international relations to emerge from the post-World War II era, said Stephen M. Walt, a Harvard University professor and former student of Dr. Waltz’s.

He had a “huge impact,” Walt said. “Even people who disagreed with him had to think about why he cast this enormous shadow over the field.”

Dr. Waltz’s books were respected for their penetrating insight and became staples of higher education. Among those classics was his first book, “Man, the State and War: A Theoretical Analysis,” published in 1959.

Kenneth N. Waltz taught at the University of California at Berkeley and Columbia University. (Bonnie Rose Schulman)

In that volume, Walt said, Dr. Waltz “essentially came up with a scheme for organizing several centuries of writing about the causes of war.” (Besides his academic research, Dr. Waltz had personal knowledge of the subject, having served in the Army in World War II and the Korean War.)

Another of his most celebrated works was “Theory of International Politics” (1979). That text, building on Dr. Waltz’s earlier work, outlined his overarching worldview. He was identified as a proponent of realism, a school of thought often associated with international relations scholar Hans Morgenthau, and argued that states had no choice but to make security and survival their top concerns.

Outside academia, Dr. Waltz drew the greatest attention for his ideas on nuclear weapons. In 1981, he published a paper titled “The Spread of Nuclear Weapons: More May Be Better.” He argued essentially that the “measured spread” of nuclear weapons would force states that wield them to behave responsibly. The weapons would be a stabilizing deterrent, Dr. Waltz posited, and make wars more difficult to spark.

Dr. Waltz advanced his theory throughout his career and was the co-author, with scholar Scott D. Sagan, of “The Spread of Nuclear Weapons: A Debate” (1995). Last year, Foreign Affairs published Dr. Waltz’s article “Why Iran Should Get the Bomb.”

“Most U.S., European, and Israeli commentators and policymakers warn that a nuclear-armed Iran would be the worst possible outcome of the current standoff,” he wrote. “In fact, it would probably be the best possible result: the one most likely to restore stability to the Middle East.”

Dr. Waltz’s critics argued that he fell prey to excessive optimism, such as when he cited Libyan leader Moammar Gaddafi as an apparently irrational leader who could, in fact, be reasoned with. “This is the kind of faith in reason that gives rationalism a bad name,” writer Leon Wieseltier argued in the New Republic last year.

Dr. Waltz took pride in calling himself a “nuclear optimist.”

“Pessimists,” he once said, “deal with hypothetical disasters that have never occurred. It seems to me that the optimists are the realists and the pessimists are the ones who are off in some ill-defined hypothesized world.”

Kenneth Neal Waltz was born June 8, 1924, in Ann Arbor, Mich. Neither of his parents graduated from high school, he recalled in an interview with U.C.-Berkeley.

Dr. Waltz came to international relations somewhat circuitously, after pursuing interests in drama, literature and mathematics. He studied math and economics at Oberlin College in Ohio, where he received a bachelor’s degree, and studied economics at Columbia University, where he received a doctorate in political science in 1954.

After his military service in the Pacific during World War II, Dr. Waltz remained in the Army Reserve and was recalled for duty in Korea, Rapp-Hooper said. He was described as an early critic of U.S. involvement in Indochina during the Vietnam War. Decades later, he spoke out against President George W. Bush and the handling of the Iraq war.

Dr. Waltz was a former president of the American Political Science Association.

His wife of 59 years, the former Helen “Huddie” Lindsley, died in 2008. He was predeceased by his son Thomas Waltz. Survivors include two sons, Daniel Waltz of Bethesda and Kenneth Waltz Jr. of Juneau, Alaska; and four grandchildren.

In discussions of nuclear policy, Dr. Waltz argued that nuclear weapons had not “proliferated” in recent decades but rather spread at a “glacial” speed.

“Deterrence has worked 100 percent of the time. We can deter small nuclear powers,” he said at an event at Columbia in 2007, according to the Journal of International Affairs. “After all, we have deterred big nuclear powers like the Soviet Union and China. So sleep well.”