The North Atlantic Treaty Organization (NATO) marks its 75th anniversary this month. The observance, part of a NATO summit hosted by the United States in Washington, D.C. [July 9-11], is a big deal, and it should be. NATO is one of the most successful and important alliances in history.

For any partnership of diverse nations to endure for 75 years is no small accomplishment. NATO has not only endured; it has thrived, and it has grown, from its original 12 members to 32 nations. It has been effective in its central missions of deterring aggression by the Soviet Union — and later by Russia — and promoting security and unity among democracies.

Ever since Russia invaded Ukraine in February 2022, there has been no question about NATO’s relevance. While Ukraine is not yet a NATO member, the alliance has rallied to its support. It’s well understood that, if Russia can win in Ukraine, the security of Europe is at risk.

And America’s security is intimately bound with Europe’s security. China may pose a greater threat; it is certainly our most significant rival. But a strong and united NATO lets the U.S. focus attention and resources on countering China’s aggression in the Asia–Pacific region.

When the United States, Canada, and 10 Western European nations created NATO, World War II had left much of Europe in ruins. More than 36 million Europeans had died — more than half of them civilians. Millions were homeless, many in refugee camps. Children wandered the streets of burned-out cities. Food shortages and power outages were frequent.

The U.S. had launched the Marshall Plan to provide material aid and rebuild Europe’s economy, and NATO was needed for the continent’s security. The Soviet Union was the primary threat, but the alliance also aimed to deter the rise of militant nationalism and promote democracy. Its key feature was Article 5, which declared that an attack on any NATO member would be considered an attack on all of them. The agreement now enhances security for nearly 1 billion people.

With the collapse of the Soviet Union, it made sense to wonder if NATO has served its purpose. The alliance had its ups and downs. Donald Trump, as president, criticized it and bashed our allies for not spending enough on defense. But new threats challenged our security, including terrorism, cyberattacks, nuclear proliferation, pandemics, and natural disasters. NATO still mattered.

Then Russia sent troops and tanks into Ukraine. NATO became the platform for coordinating the European and North American response.

At this month’s summit of NATO heads of state, affirming unwavering support for Ukraine [was scheduled to] top the agenda. Ukraine participated through the NATO-Ukraine Council, launched last year. In an important transition, Jens Stoltenberg steps down after 10 years as secretary-general and is being replaced by Mark Rutte, prime minister of the Netherlands.

President Joe Biden has aptly called NATO “the greatest military alliance in the history of the world,” and we’re right to celebrate its history. At the same time, we need to ensure the alliance continues to safeguard our security in the future. And there are reasons for concern.

Russia’s war in Ukraine, should it succeed, could embolden Vladimir Putin to threaten more of Europe. The increasing cooperation by Russia, China, and North Korea — all of them nuclear-armed — is worrisome. Recent years have seen the growth of militant nationalism in Europe, one of the trends NATO was founded to counter. Trump’s “America First” movement has reawakened the American isolationism that was prevalent before World War II.

It’s often said that eternal vigilance is the price of liberty. NATO and other alliances keep us vigilant about our freedom and security, and we should do our best to maintain and strengthen them.                  

Lee Hamilton, 93, is a senior advisor for the Indiana University (IU) Center on Representative Government, distinguished scholar at the IU Hamilton Lugar School of Global and International Studies, and professor of practice at the IU O’Neill School of Public and Environmental Affairs. Hamilton, a Democrat, was a member of the U.S. House of Representatives for 34 years (1965-1999), representing a district in south-central Indiana.