Forty-one years ago, in the shadow of the Vietnam War, Michael Walzer published Just and Unjust Wars, an exploration of the morality of going to war and of war-fighting—a 20th-century update on the old problems of jus ad bellum and jus in bello. A professor at Harvard and Princeton University and long a member of the idiosyncratic left-wing intellectual crowd around Dissent magazine, Walzer established himself as an original thinker and laid the predicate for his lifelong willingness to call out fellow leftists as necessary for the sloppiness or shoddiness of their often abstract moral reasoning on matters of war and peace.

Vietnam was an unjust war, in Walzer’s view, one that should never have been fought. But for him, it hardly followed that all wars are unjust. At a time when a kind of nihilist pacifism was taking hold among many on the left, Walzer insisted on reminding his comrades of the moral necessity of World War II and the struggle to defeat fascism. Similarly, at a time when many of his contemporaries were apologizing for, if not celebrating, brutal regimes emerging in postcolonial states where liberation movements had thrown off an imperial yoke, Walzer insisted on holding these governments accountable for their misdeeds. And even as many on the left were working up a post-Marxist critique of neo-imperialist America as a malevolent force in international politics, Walzer insisted that some wars America might wage, including armed interventions for humanitarian purposes, could still be just.

Now, at the age of 83, he has produced a slender new volume, A Foreign Policy for the Left, consisting mostly of material reworked from articles of consequence he published previously, mostly in Dissent. This effort offers not comprehensive foreign-policy prescriptions but rather a comprehensive way of thinking about foreign policy from his point of view—that of a stalwart man of the left.

Why not, one wonders, a simpler title or even a broader one? Perhaps A Foreign Policy for America or Justice in Foreign Policy? Walzer is certainly a personage venerable enough to speak to all Americans, whether they end up agreeing with his policy principles or not. Yet he has chosen quite deliberately to write for a narrower audience—“for the left.” The striking reason for this becomes apparent through the course of the book: It’s because the left, in his view, needs more persuading before it can be said to have possession of foreign-policy principles that are intellectually and morally defensible.

Walzer is a polemicist in form true to the word’s origin. One can describe his writing over the course of an illustrious career as not only an argument for the conclusions he has come to, but also as an “attack” on the erroneous conclusions of others. In Just and Unjust Wars, his enemy is the remark frequently attributed to Civil War general William Tecumseh Sherman: “War is hell”—meaning that considerations of morality cannot really enter into the discussion once one decides to wage it. Just and Unjust Wars is a book-length rebuttal beginning with the observation that even in hellish times, human beings can and do consider what they ought to do, taking their own moral reasoning as an important guide.

The attack in the new book is on what Walzer calls the “default” view of those on the left, namely, “an almost exclusive focus on how we and our fellow citizens live when we are among ourselves. For many of us, the only good foreign policy is a good domestic policy. Americans will be more safe in the world, and the world will be better off, leftists have repeatedly argued, if we concentrate on creating a just society at home.”

In service to this preference, the left has been too prone to give in to “the politics of pretending”—taking the world and the challenges it poses to be something other that what they are. Leftists have developed a number of “shortcut” arguments to which they can easily repair rather than undertaking the harder work of moral reasoning that real-world cases require. First among the shortcuts Walzer identifies is an almost instinctive tendency to think of the oppressed as “angels”—leading to a likewise reflexive tendency to side with leaders speaking in their name, and therefore to refrain from according the latter the moral scrutiny they warrant. Second is the imperative to stand up against “imperialism”—and therefore to oppose much if not all action abroad by the latter-day hegemon, the United States. Third is to blame Israel as the source of almost all troubles in the world’s most troubled region, the Middle East. Fourth is, regardless of the circumstances, “to support every government that sets itself against American interests”—which actually seems to be an amalgam of shortcuts one and two.