The broad reasons behind their relative ease are twofold. First, millennials grew up after the Cold War, in the absence of a superpower confrontation and the specter of nuclear holocaust. Terrorism is certainly dangerous, but it has not fueled the same level of fear that the Cold War did. Many millennials were simply too young for 9/11 to have had the direct emotional impact it did for older Americans.

In fact, the youngest millennials, born after 1987, are significantly more sanguine about global threats than older millennials, more supportive of the Iran nuclear deal, and less concerned about whether Iran might develop nuclear weapons someday.

Second, the meaning and impact of 9/11 have become entangled with the U.S. response to it. A majority of millennials, as with other generations, views the wars in Afghanistan and Iraq as a mistake, but millennials are also the least likely to believe that using military force is the best way to solve problems. For millennials, 9/11 demonstrates less that the world is a dangerous place than that that aggressive U.S. military action is counterproductive.

And that’s a big reason millennials support the Iran deal: It represents a diplomatic approach to the Mideast that breaks from the military‐​focused policies of the recent past. When asked whether Congress should allow the nuclear deal to move forward, 58 percent of millennials said it should, compared with 49 percent of older Americans. Millennials are also the only generation in which a majority believes that the plan will either delay or stop Iran from developing nuclear weapons.

Those tempted to argue that these results reflect liberal millennials taking cues from Obama are wrong. Though partisanship is certainly alive and well among millennials, it has much less impact on their attitudes toward the Iran deal than it does on the attitudes of older Americans.

The partisan support gap is just 16 percentage points among millennials, with 75 percent of millennial Democrats and 59 percent of millennial Republicans supporting the deal. But among Gen Xers, born between the 1960s and the early 1980s, the gap between Democrats and Republicans is 53 points; among baby boomers, the gap is 48 points; and among the silent generation (1920s‐​1940s), the gap is a whopping 72 percentage points. In short, millennials are taking fewer cues than their elders from their political parties.

These findings are the bow wave of a sea change ahead in American politics. The millennial position on Iran is not a blip but an emerging pillar of U.S. public opinion on foreign policy. Millennials’ attitudes toward threats, the utility of military force, the importance of allies, and the role of diplomacy were formed in what sociologists call the “critical period,” the time between the ages of roughly 14 and 24 when historical context and major events shape worldviews and attitudes for a lifetime.

These views are already shaping opinions on a wide range of issues, from the Middle East to climate change and the rise of China. And with millennials now outnumbering baby boomers, we can expect to see their attitudes and opinions playing an increasingly important role in the development and conduct of U.S. foreign policy.