Editor's note: The following column first appeared in The Washington Post.

When Donald Trump ran for president, he criticized the interventionist policies of his Republican and Democratic predecessors, sparking fears that he would usher in a new era of American isolationism. But at the U.N. this week, Trump laid out a clear conservative vision for vigorous American global leadership based on the principle of state sovereignty.

Judging from their hysterical reaction, critics on the left now seem to fear he’s the second coming of George W. Bush. Sen. Dianne Feinstein (D-Calif.) called his address “bombastic.” Rep. Barbara Lee (D-Calif.) said it represented an “abdication of values.” And Hillary Clinton said it was “very dark” and “dangerous.” This is all the standard liberal critique of conservative internationalism. The left said much the same about President Ronald Reagan.

In New York, Trump called on responsible nation-states to join the United States in taking on what he called the “scourge” of “a small group of rogue regimes that . . . respect neither their own citizens nor the sovereign rights of their countries.” This mission can be accomplished, Trump said, only if we recognize that “the nation-state remains the best vehicle for elevating the human condition.”

He is right. Communism and fascism were not defeated by the United Nations, and global institutions did not fuel the dramatic expansion of human freedom and prosperity in the past quarter-century since the collapse of the Soviet Union. What has inspired and enabled the spread of peace, democracy and individual liberty was the principled projection of power by the world’s democratic countries, led by the United States.

This is what is needed today — and what Trump promised in his address. He recast his “America First” foreign policy as a call not for isolationism but for global leadership by responsible nation-states. He embraced the Marshall Plan — the massive U.S. effort to support Europe’s postwar recovery. And he declared that “if the righteous many do not confront the wicked few, then evil will triumph” because “when decent people and nations become bystanders to history, the forces of destruction only gather power and strength.”

Trump then used this theme of sovereignty to challenge the United States’ two greatest geopolitical adversaries, China and Russia, insisting that “we must reject threats to sovereignty from the Ukraine to the South China Sea.”

The president also had a blunt message for North Korea. He dismissed its leader, Kim Jong Un, as “Rocket Man” and said Kim “is on a suicide mission for himself and for his regime.” He made clear that “the United States has great strength and patience, but if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea.” This message rattled some, and that was its intent. During the Cold War, Soviet leaders truly believed that Reagan was preparing for war and might actually launch a first strike. This belief is one of the reasons that a cataclysmic war never took place.

If we hope to avoid war with North Korea today, the regime in Pyongyang must be made to believe and understand that Trump is in fact, as he said at the U.N., “ready, willing and able” to take military action. His tough rhetoric was aimed not just at Pyongyang but also at China and other states whose cooperation in squeezing the regime is necessary for a peaceful solution. Those words must be followed by concrete steps short of total destruction to make clear that he is indeed serious and that North Korea will not be permitted to threaten American cites with nuclear annihilation.

Trump also put himself squarely on the side of morality in foreign policy and explicitly stood with those seeking freedom around the world. He promised to support the “enduring dream of the Cuban people to live in freedom.” He declared that “oppressive regimes cannot endure forever” and upbraided the Iranian regime for masking “a corrupt dictatorship behind the false guise of a democracy” while promising to stand with “the good people of Iran [who] want change.” He took on Iran’s ally, “the criminal regime of Bashar al-Assad” in Syria, whose “use of chemical weapons against his own citizens, even innocent children, shock the conscience of every decent person.”

And his best moment came when he turned to what he called the “socialist dictatorship” of Nicolás Maduro, declaring that “the problem in Venezuela is not that socialism has been poorly implemented, but that socialism has been faithfully implemented.” Trump promised to help the Venezuelan people “regain their freedom, recover their country and restore their democracy.”

This is classic conservative internationalism: a vigorous defense of freedom, a bold challenge to dangerous dictators and a commitment to the principle of peace through strength. No wonder Trump’s critics on the left are so upset.