Archbishop Desmond Tutu, who died on Sunday at age 90, had a genius for speaking truths that the powerful tried to avoid hearing. When he delivered his 1984 Nobel Lecture, for instance, it was understood that the Anglican priest would condemn the apartheid system that codified racial hatred and violence in his homeland of South Africa—and similar systems of racial, social, and economic injustice globally. But Tutu didn’t stop there. He seized the platform to decry the international military-industrial complex that extended from, underpinned, and maintained that injustice.

“I have spoken extensively about South Africa, first because it is the land I know best, but because it is also a microcosm of the world and an example of what is to be found in other lands in differing degree—when there is injustice, invariably peace becomes a casualty,” declared the archbishop of Cape Town.

In El Salvador, in Nicaragua, and elsewhere in Latin America, there have been repressive regimes which have aroused opposition in those countries. Fellow citizens are pitted against one another, sometimes attracting the unhelpful attention and interest of outside powers, who want to extend their spheres of influence. We see this in the Middle East, in Korea, in the Philippines, in Kampuchea, in Vietnam, in Ulster, in Afghanistan, in Mozambique, in Angola, in Zimbabwe, behind the Iron Curtain.

Because there is global insecurity, nations are engaged in a mad arms race, spending billions of dollars wastefully on instruments of destruction, when millions are starving. And yet, just a fraction of what is expended so obscenely on defense budgets would make the difference in enabling God’s children to fill their stomachs, be educated, and given the chance to lead fulfilled and happy lives. We have the capacity to feed ourselves several times over, but we are daily haunted by the spectacle of the gaunt dregs of humanity shuffling along in endless queues, with bowls to collect what the charity of the world has provided, too little too late. When will we learn, when will the people of the world get up and say, Enough is enough. God created us for fellowship. God created us so that we should form the human family, existing together because we were made for one another. We are not made for an exclusive self-sufficiency but for interdependence, and we break the law of our being at our peril. When will we learn that an escalated arms race merely escalates global insecurity? We are now much closer to a nuclear holocaust than when our technology and our spending were less.

Arguing that “we are on the road inexorably to self-destruction, we are not far from global suicide; and yet it could be so different,” Tutu preached a gospel of peace and reconciliation. Yet his was not a soft advocacy for avoiding conflict. Tutu went out of the way to identify the sources of violence, especially those responsible for the nuclear arms race.

In a 2017 essay for The Nation, he recalled: “When Nelson Mandela walked free, in 1990, after 27 grueling years behind bars, South Africa began the process of emancipating itself from not only from its brutal apartheid regime but also its arsenal of atomic bombs. Like white-minority rule, these awful weapons had weighed heavily on us all, entrenching our status as a pariah nation. Their abolition was essential for our liberation.”

In that essay, Tutu issued a call to action on behalf of a global treaty to prohibit nuclear weapons under international law. “With sabres rattling and the specter of nuclear war looming large,” he wrote, “the imperative to abolish man’s most evil creation—before it abolishes us—is as urgent as ever. Further arms races and provocations will lead us inexorably to catastrophe.”

What was particularly striking in Tutu’s activism was his determination to call out the powerful nations that claimed to be “responsible” nuclear powers. “All of those who wield nuclear weapons are deserving of our scorn,” he asserted. “The development and stockpiling of weapons of mass destruction by any state is morally indefensible. It breeds enmity and mistrust and threatens peace. The radiation unleashed by an American or British or French nuclear bomb is just as deadly as that from a North Korean one. The inferno and shock waves kill and maim no less indiscriminately.”

It is the archbishop’s willingness to call out the powerful, in the fight against apartheid and in the struggle against war and militarism, that we would do well to recall as we honor his rich legacy as a moral leader.

Tutu was specific in opposing illegal and unnecessary wars, as he did in the days before the United States–led invasion and occupation of Iraq in 2003. Speaking at Marquette University in Milwaukee, where he was receiving the prestigious Père Marquette Discovery Award on the eve of the invasion, Tutu concluded his remarks with an impassioned embrace of the anti-war movement:

God weeps as God looks on what we are doing, on what we are contemplating doing to one other. The just war theory, amongst other things, postulates that a legitimate authority declares and wages war. A war against Iraq declared unilaterally by the United States would be one not declared by a legitimate authority and so would be immoral. God smiles through the tears to see the many who oppose this war.

This is a great, great country, a generous country, a compassionate country, a country that helped Nelson Mandela come out of prison, a country which helped make South Africa free and democratic. That is your legacy, your tradition. Why want to tarnish it with a war most of the world opposes? Help to wipe the tears from God’s eyes. For God says, “Yes you and you and you, you can make a difference. You can help me realize my dream that my children, my children, you are family.”

Almost a decade later, the archbishop refused to participate in a conference in Johannesburg because former British prime minister Tony Blair was scheduled to appear. Tutu explained that Blair and former President George Bush had “fabricated the grounds to behave like playground bullies and drive us further apart.”

Instead of enjoying the lucrative spoils of the international speaking circuit, Tutu said the former prime minister and former president should be tried before the International Criminal Court in The Hague. Recounting Bush and Blair’s record of deceit and destruction, the Nobel Peace Prize recipient argued, “On these grounds, alone, in a consistent world, those responsible should be treading the same path as some of their African and Asian peers who have been made to answer for their actions in The Hague.”

Archbishop Tutu campaigned for a consistent world, where all leaders were held to account for their actions, and where advocacy for peace and justice was paramount. This was his great faith and his great promise. Decrying the presidents, prime ministers, and weapons merchants who “have held humankind to ransom,” he counseled against deferring to the powerful. Rather, he insisted that it would fall to the people to claim “their right to live in a safe, harmonious global community, unburdened by this ultimate menace.”

“Of course, it was not the slave owners who led the struggle to abolish slavery. Nor was it the Afrikaners who tore down the system of apartheid in South Africa. The oppressed fought for, and ultimately secured, their own freedom,” he explained in his 2017 essay. “Through collective action, we built the foundations for transformative change, to the benefit of all.”