I was in Kyiv last week for my fourth visit to Ukraine as Secretary of Defense. And being in Kyiv always drives home the enormity of the stakes in Ukraine's fight for freedom.

We must never forget how this war began. For years, Russian President Vladimir Putin had harassed and assaulted the independent nation-state of Ukraine. On February 24, 2022, he crossed the line into all-out invasion, and the Kremlin started the largest war in Europe since World War II.

When the largest military in Europe becomes a force of aggression, the whole continent feels the shock. When a permanent member of the UN Security Council tries to deny self-rule to more than 40 million people, the whole world feels the blow. And when a dictator puts his imperial fantasies ahead of the rights of a free people, the whole international system feels the outrage.

That's why nations of goodwill from every corner of the planet have risen to Ukraine's defense. And that's why the United States and our allies and partners have proudly become the arsenal of Ukrainian democracy. America's values call us to stand by a peaceful democracy fighting for its life. And America's security demands that we stand up to Putin's aggression.

Ukraine matters to U.S. security for four blunt reasons. Putin's war is a direct threat to European security, a clear challenge to our NATO allies, an attack on our shared values, and a frontal assault on the rules-based international order that keeps us all safe.

Yet after nearly 1000 days of war, Putin hasn't achieved a single one of his strategic objectives. Ukrainian President Volodymyr Zelensky didn't flee. Kyiv didn't fall. And Ukraine didn't fold.

Instead, Russia has paid a staggering price for Putin's imperial folly, with hundreds of thousands of Russian casualties since February 2022 and more than $200 billion squandered. According to the Center for Strategic and International Studies, Russian losses in just the first year of Putin's war were more than Moscow's losses in all of its conflicts since World War II -- combined.

Ukraine has suffered terribly at Putin's hands. But as I saw again in Kyiv last week, Ukraine stands unbowed -- and even strengthened. Ukraine's fight began with soldiers setting tank traps on the streets of Kyiv and ordinary citizens making Molotov cocktails to defend their homes. It continues today with a battle-tested Ukrainian military and security forces -- and a roaring Ukrainian defense industrial base. Ukrainian factories are now pumping out some of the best drones in the world, and experienced Ukrainian air defenders are protecting their forces and their families.

Since April 2022, I have been convening the Ukraine Defense Contact Group -- a coalition of some 50 countries from around the world determined to help Ukraine fight Putin's aggression. The Contact Group has met 24 times now, and its members have provided more than $51 billion in direct security assistance to Ukraine.

I'm proud that the United States is doing our part, committing more than $58 billion in security assistance to Ukraine and delivering two Patriot batteries, other air defense systems, 24 HIMARS rocket systems, thousands of armored vehicles, and millions of rounds of artillery. This is a very real financial commitment. But for anyone who thinks that American leadership is expensive, consider the price of American retreat. In the face of aggression, the price of principle is always dwarfed by the cost of capitulation.

America's allies and partners are sharing the burden of our common security. As a percentage of GDP, a dozen U.S. allies and partners now provide more security assistance to Ukraine than the United States does. Germany alone has provided or committed to military assistance to Ukraine valued at close to $31 billion. And through the Contact Group and its "capability coalitions," Ukraine's friends are now forging an unprecedented, coordinated, 13-country drive to increase industrial production, meet Ukraine's battlefield requirements, and build up the Ukrainian force to deter and repel Russian aggression in the future. Not since World War II has America systematically rallied so many countries to provide such a range of industrial and military assistance for a partner in need.

There is no silver bullet. No single capability will turn the tide. No one system will end Putin's assault. What matters is the combined effects of Ukraine's military capabilities -- and staying focused on what works.

The spirit of Ukraine has inspired the world. It has reminded us all to never take our freedom for granted. We fully understand the moral chasm between aggressor and defender. We will not be gulled by the frauds and falsehoods of the Kremlin's apologists. And we will continue to defend the Ukrainian people's right to live in security and freedom.

Putin's assault is a warning. It is a sneak preview of a world built by tyrants and thugs -- a chaotic, violent world carved into spheres of influence; a world where bullies trample their smaller neighbors; and a world where aggressors force free people to live in fear.

So we face a hinge in history. We can continue to stand firm against Putin's aggression -- or we can let Putin have his way and condemn our children and grandchildren to live in a far bloodier and more dangerous world. If Ukraine falls under Putin's boot, all of Europe will fall under Putin's shadow. Putin is not just hammering at the norms of the international system built at such terrible cost by the Allies after World War II. He is shoving us all toward a world where might makes right and where empire trumps sovereignty. So we must continue to squarely face the specter of today's aggressive Russia, backed by other autocrats, from North Korea to Iran.

Peace is not self-executing. Order does not preserve itself. And the principles of freedom, sovereignty, and human rights do not uphold themselves. So U.S. President Joe Biden has chosen the path of mutual responsibility and common security.

Ukraine does not belong to Putin. Ukraine belongs to the Ukrainian people. And Moscow will never prevail in Ukraine.

Putin thought Ukraine would surrender. He was wrong. Putin thought our democracies would cave. He was wrong. Putin thought the free world would cower. He was wrong. And Putin thinks he will win. He is wrong.

As a military man, I've learned to never underestimate the strategic advantage of a just cause. And I've learned that free people will always refuse to replace an open order of rules and rights with one dictated by force and fear.