Austin made the remarks at the annual Halifax International Security Forum, which attracts defense and security officials from Western democracies.

“Russia’s invasion offers a preview of a possible world of tyranny and turmoil that none of us would want to live in. And it’s an invitation to an increasingly insecure world haunted by the shadow of nuclear proliferation,” Austin said in a speech.

“Because Putin’s fellow autocrats are watching. And they could well conclude that getting nuclear weapons would give them a hunting license of their own. And that could drive a dangerous spiral of nuclear proliferation.”

Austin dismissed Putin’s claims that “modern Ukraine was entirely created by Russia,” calling it a vision of “a world in which autocrats decide which countries are real and which countries can be snuffed out.”

He added that the war “shows the whole world the dangers of disorder. That’s the security challenge that we face. It’s urgent, and it’s historic.

But we’re going to meet it. ... The basic principles of democracy are under siege around the world,” he said.

U.S. President Joe Biden last month declared that the risk of nuclear “Armageddon” is at the highest level since the 1962 Cuban missile crisis; Russian officials have raised using tactical nuclear weapons after suffering massive setbacks in the nearly nine-month invasion of Ukraine.

While U.S. officials for months have warned of the prospect that Russia could use weapons of mass destruction in Ukraine in the face of battlefield setbacks, Biden administration officials have repeatedly said nothing has changed in U.S. intelligence assessments to suggest that Putin has imminent plans to deploy nuclear weapons.

CIA Director Bill Burns recently met with his Russian intelligence counterpart to warn of consequences if Russia were to deploy a nuclear weapon in Ukraine.

Austin said nuclear weapons need to be responsibly controlled, and not used to threaten the world.

“Ukraine faces a harsh winter. And as Russia’s position on the battlefield erodes, Putin may resort again to profoundly irresponsible nuclear saber-rattling,” he said

Austin also compared Russia to China, saying Beijing is trying to refashion both the region and the international system to suit its authoritarian preferences. He noted China’s increasing military activities in the Taiwan Strait.

“Beijing, like Moscow, seeks a world where might makes right, where disputes are resolved by force, and where autocrats can stamp out the flame of freedom,” he said.

Austin called Putin’s invasion the worst crisis in security since the end of the Second World War and said the outcome “will help determine the course of global security in this young century,” Austin said..

Austin said the deadly missile explosion in Poland this week is a consequence of Russian President Vladimir Putin’s “war of choice” against Ukraine. “The tragic and troubling explosion in Poland this week reminded the whole world of the recklessness of Putin’s war of choice,” Austin said.

On Tuesday, two workers were killed when a projectile hit a grain-drying facility close to Poland’s border with Ukraine. While the source of the missile is under investigation, NATO officials have said they suspect it was fired from a Ukrainian missile battery.

Officials from Poland, NATO and the United States have blamed Russia for the deaths in any case, saying a Ukrainian missile would not have misfired had the country not been forced to defend itself against heavy Russian attacks that day.

Russian officials have cast the conflict as a struggle against NATO — though Ukraine is not a NATO member even if it has been receiving aid from NATO member states.

Austin said NATO is a defensive alliance and poses no threat to Russia.

“Make no mistake: we will not be dragged into Putin’s war of choice. But we will stand by Ukraine as it fights to defend itself. And we will defend every inch of NATO territory,” Austin said.

A Polish investigation to determine the source of the missile and the circumstances of the explosion was launched with support from the U.S. and Ukrainian investigators joined the probe on Friday.

Andriy Yermak, head of the Office of the President of Ukraine, said in an interview broadcast live at the forum that “It’s not right to say it’s a Ukrainian rocket, or a Russian rocket, before the investigation is over.”

In its 14th year, about 300 people gather each year at Halifax International Security Forum held at Halifax’s Westin hotel, where about 13 Ukrainian refugees now work.