I teach international relations. Few fields have undergone more change over the past 25 years than the study of world politics. Humanity has gone from sheer euphoria one moment — on 11/9 (the fall of the Berlin Wall on Nov. 9, 1989, marking the end of the Cold War and the triumph of liberal democracy over communism) — to sheer terror the next – on 9/11 (the destruction of the World Trade Center in New York City in 2001, ushering in a new, darker chapter in global violence and a newfound sense of vulnerability for liberal democracies). 

The most profound change has occurred in the very nature of war. For much of the 20th century, and indeed much of world history over the past 400 years, the primary security concern among nations was interstate war, particularly war between “great powers” that tended to widen into a systemwide conflict, as with World War I and World War II, which together claimed more than 80 million lives. 

Thankfully, there has been a dramatic decline in the frequency of interstate war and a virtual disappearance of great-power war. The period since 1945 has been called the long peace, the longest stretch of time since the birth of the modern nation-state system in the 17th century during which major powers have not exchanged hostilities. 

Recall that the Cold War was not a shooting war, even though the Cuban missile crisis and other crises tested the ability of the Americans and Russians to practice self-restraint. Although some see a possible revival of the Cold War given Russia’s aggression in Ukraine and elsewhere under Vladimir Putin, the probability of Washington and Moscow resorting to armed force against each other is close to zero.

Steven Pinker, commenting not just on the absence of great-power war but on the rarity of classic interstate war generally today, has concluded, in “The Better Angels of Our Nature,” that “war is really going out of style.” Similarly, Gregg Easterbrook has said, in “The End of War?” that “it is possible that a person’s chance of dying because of war has become the lowest in human history.” 

They are not alone in making such statements, even if those observations might seem incompatible with daily news headlines from the Middle East and other locales. 

That’s the good news: the decrease in large-scale, all-out, sustained armed combat between organized, uniformed national armies across well-defined frontiers. 

The bad news is that when interstate violence does occur, it tends to mix with intrastate violence (civil war) and extrastate violence (transnational terrorism) in complex conflagrations, as in Iraq and Afghanistan, which can be harder to manage and terminate.   

So, although humanity has made progress in curbing hostilities, war is not yet quite “on its last legs,” as Ralph Waldo Emerson predicted in 1849 and Pinker and others speculate about in the early 21st century.   

Arguably, today the main security threat to the United States as well as much of the world is “the war on terror.” Since the war on terror has no conceivable end — it is unlikely we will ever capture or kill the last terrorist and have a peace treaty ceremony held on board a ship à la the USS Missouri in 1945 — it has been called by the Pentagon the long war.

The war on terror not only lacks clear temporal boundaries but also lacks clear geographical, spatial boundaries. In “Dirty Wars,” journalist Jeremy Scahill criticizes the United States for “making the world a battlefield” in terms of claiming the right to engage in a limitless use of military force in “a borderless global war.” 

Likewise, a recent New York Times editorial (March 20) criticized the United States for its drone strikes outside the “hot” battlefields of Afghanistan, Syria and Iraq, extending their use to relatively peripheral areas such as Pakistan, Libya, Yemen and Somalia. 

However, the latter four countries surely harbor terrorists (ISIS, al-Qaida, Boko Haram and others) who pose a threat to America and its allies, along with innocent people worldwide. Given the recent terrorist attack on the Brussels airport and subway system that killed or wounded more than 300 people, is not Belgium part of the “battlefield” in the war on terror?

Are Scahill and the Times seriously suggesting that if, say, American intelligence located the mastermind of the Brussels attack in Libya, and there is reason to believe another terrorist plot is being planned, we should dispatch police to arrest that individual, read him his Miranda rights, and return him for trial in a court of law in the United States or Belgium so that he could get due process, as opposed to eliminating this “enemy combatant” with a well-placed missile? 

In other words, should we be treating the war on terror as a mere criminal-justice matter, as opposed to the national security threat that it is? 

I once asked the distinguished South African jurist Richard Goldstone at a Yale Club event whether he felt the United States had a legal right to kill the American cleric Anwar al-Awlaki with a drone strike in Yemen in 2011, because  he had inspired three of the 9/11 skyjackers and was promoting further terrorist attacks through social media. Judge Goldstone said it qualified as self-defense under the laws of war, even if critics called it “summary execution” or “assassination.” 

I have recently written a book on “the new warfare” that explores an existential dilemma faced by countries such as the United States and Israel: How can these states be expected to fight “cleanly,” complying with the Geneva Conventions and international humanitarian law — and still win — when typically they are now up against an ostensibly weaker adversary like ISIS that tries to level the playing field by observing no rules whatsoever? 

We need to continue to honor the rule of law and human rights domestically and internationally as much as possible but, in the current international system, that is easier said than done. It is not enough to argue that the terrorists win if we are forced to sacrifice our basic values. They may well win if we do not at least aim for a realistic balance between civil liberties and other treasured rights on the one hand and security and survival on the other. 

I would just add that, amid all the change we are coping with, there is one constant: the ongoing apathy and ignorance of large swaths of the American public regarding the outside world. Relatively few Americans are even aware of the issues raised here, much less informed about them. There has been precious little serious discussion of foreign policy by any of the presidential candidates. 

Perhaps, unfortunately, it might take another 9/11 on our shores to awaken the body politic.