Israel's wildly disproportionate act of violence against mostly unarmed protesters in the Gaza Strip — killing more than 60 and injuring well over 1,000 with live ammunition while suffering not one significant casualty of its own — is a dark moment for a region with more than its share of suffering. It's also the latest in a series of signs that the brief period in which the world had reason to hope that warfare was being hemmed in by moral considerations may well be drawing to a close.

Welcome to the post-just-war world.

For most of human history until quite recently, combatants in war did pretty much whatever they thought they needed to do to win. This was true for the "good guys" no less than the "bad." In World War II, the United States and Great Britain firebombed the center of cities, incinerating their civilian populations, and of course they also dropped atomic bombs on Hiroshima and Nagasaki, killing something in the vicinity of 200,000 people. In Vietnam, the U.S. pummeled the northern part of the country with explosives and napalmed huge swaths of the jungle in which the Viet Cong lived and preferred to fight. The result? Roughly 1.1 million North Vietnamese civilians and Viet Cong fighters dead.

This began to change only in the 1970s, when the human rights movement gained traction in convincing the United States military of the importance of abiding by the strictures of just-war theory. The military's motives were not pure. The Pentagon realized that, in an age of mass media, a failure to act with restraint could lead to awful press coverage and therefore hand a potent propaganda victory to our primary geopolitical rival, the Soviet Union.

The rise of just-war thinking had mixed results. I've written quite critically about the way that just-war considerations about when to go to war (jus ad bellum) can be used to make wars more likely, by encouraging those in positions of power to believe that they have objective moral criteria on their side. But the other half of just-war thinking (jus in bello), which concerns how a war is conducted once it is underway, has unquestionably had positive consequences, leading to efforts to distinguish legitimate (usually military) targets from illegitimate (usually civilian) ones, as well as inspiring serious thinking about proportionality in the use of force (with legitimacy defined as the use of the minimum amount of force required to prevail in a conflict).

Since the end of the Cold War, America's long series of wars (in the Persian Gulf and its aftermath of policing no-fly zones over Iraq; in the former Yugoslavia; in Afghanistan; in the Iraq invasion and occupation; in Libya; in Barack Obama's multi-nation drone-war campaign) have been governed by just-war criteria. Yes, civilians have been killed. But America has worked hard to minimize these deaths — as much for the sake of winning hearts and minds in the countries concerned as out of moral considerations.

Yet this relatively recent change in the way war is waged may already be coming to an end.

Now, just-war theory was never consistently followed outside of the West. The Soviet Union didn't restrain itself in its own war in Afghanistan. The wars in the former Yugoslavia during the 1990s were vicious. The Syrian civil war, like the wars that have ravaged parts of Africa in recent decades, has been a bloody mess. And of course the whole point of terrorism is to inflict maximum harm on civilian populations. It's the diametric opposite of waging war justly.

Just-war constraints have mainly been followed by the U.S. and its allies, NATO (which is led by the U.S.), and the U.N. (which, when it acts militarily, is also led by the U.S.). It was a choice by these actors on the world stage to impose constraints on themselves — to model a more humane form of warfare in the hope that they could then encourage its spread to other places through a mixture of rhetorical shaming and legal coercion in the form of war-crimes tribunals for violations of international humanitarian law.

But the effort appears to be waning. Saudi Arabia's war on Iranian proxies in Yemen has been savage, and the U.S. (beginning during the Obama administration) has supported it. Under President Trump, civilian casualties have spiked — a direct consequence of relaxed rules of engagement that allow commanders in the field to choose targets with less regard for the humanitarian consequences. (It's true that we have now twice bombed Syria in the name of punishing Bashar al-Assad for violations of the ban on using chemical weapons, but doing so was its own violation of different aspects of international law — the ones that preclude any state from acting as enforcer of international law without receiving the prior authorization of the U.N. Security Council.)

This is nothing compared to Israel's recent behavior in the Gaza Strip — and the Trump administration's reaction to it. Rather than issue a blandly supportive statement for Israel that included strong language about the need for restraint, let alone a rebuke for going too far in firing live rounds at mostly unarmed civilians, the administration declared that responsibility for the dozens of deaths and many hundreds of injuries fell squarely on Hamas, the Islamist party that governs Gaza, rather than on soldiers from the Israeli Defense Forces who opened fire on the crowd.

If the administration took any notice of just-war considerations, it would never have issued such a statement. The same could be said of Israel's defenders in the American media who rushed to declare the actions of the Jewish State fully justified in order to prevent Israeli casualties. Just-war theory demands that nations use the minimum force necessary to prevail in a conflict, not that they use the minimum force necessary to ensure that they suffer zero casualties. If the latter were acceptable criterion, then literally any military act, no matter how savage, could be morally justified — now and on into an indefinite future. After all, a nation can never know for sure that its adversaries in a conflict won't return to fight more potently in the future — and that would seem to legitimize preemptive action to neutralize them.

Instead of encouraging restraint, the American administration and Israel's cheerleaders are encouraging its opposite: unrestrained acts of war.

This won't keep other nations from denouncing Israel's actions. But international affairs is an arena defined by power, and these critics are comparatively weak. Russia doesn't want its actions constrained by moral considerations. Neither does China. Or the other nations of the Middle East. The Europeans feel differently, but without the U.S. backing them up they are powerless to do more than issue sternly worded but ultimately impotent statements.

The chilling fact is that if the U.S. gives up on holding the countries of the world to a stringent moral standard in their conduct of war, those constraints will vanish in an instant.

We are living through that instant right now. What awaits us on the other side may be every bit as bloody as the history that led us in the first place to long for the imposition of moral limits on war.