Munich – A few years after World War II, when the North Atlantic Treaty was ratified in the United States and our relationship with Europe was cemented, President Harry Truman said simply, “The more closely the nations of the Atlantic community can work together for peace, the better for all people, everywhere.”

The decades since have proven him right. And, as our trans-Atlantic relationship has grown both stronger and more expansive, so has democracy, prosperity and stability in Europe, the United States and around the globe.

But, though the trans-Atlantic relationship today is as strong and as critical as ever, there is no question that we are in the midst of a defining moment for our partnership.

We are facing multiple tests, two of which are especially worthy of attention, because they test international law, multilateral mechanisms, and the global order that we have spent the last 70 years working to build and maintain.

The first test is obviously Ukraine, where Russia has endangered the security landscape of Eastern and Central Europe, first through its illegal occupation of Crimea and now through its overt and brazen effort to destabilize eastern Ukraine.

This challenge recently led me back to Kiev to meet with President Petro Poroshenko, Prime Minister Arseniy Yatsenyuk and Foreign Minister Pavlo Klimkin, while German Chancellor Angela Merkel and French President François Hollande visited Kiev and then Moscow in pursuit of a plan to de-escalate the situation.

We all agree that military force will not end this challenge and that diplomacy will.

But the longer it takes, the more the world will have no choice but to raise the costs to Russia and its proxies. The U.S., France, Germany, and our allies and partners will stand together in support of Ukraine and in defense of the fundamental principle that international borders must not be changed by force, in Europe or anywhere else. There is no division among us whatsoever on this fundamental conviction.

The second major test is the rise of violent extremism. The Islamic State group’s recent video showing the brutal immolation of a captured Jordanian pilot represented a new low in depravity. And last week, the United Nations reported what so many already knew: that this evil group crucifies children, buries them alive and uses mentally disabled young people as suicide bombers.

Islamic State is not alone among extremists. Last month, Pakistani officials showed me time-stamped photos of the Army Public School in Peshawar before and after the Taliban killed 145 people (including 132 children) in December. The school’s assembly hall, filled with students sitting attentively in their chairs, was transformed into a death chamber — blood, broken eyeglasses, scattered textbooks, torn jackets and lifeless young bodies.

The school’s principal tried to save her students. When challenged by the murderers, she pointed to the children and said, “I am their mother.” Those were her last words.

The world cannot and will not wilt in the face of such extremism, wherever it exists, whether in the Sahel, Nigeria, Iraq or Syria.

Today, the international coalition fighting Islamic State has grown to more than 60 active members. Since September, we have retaken 700 square km of territory.

We have deprived the group of the use — and resulting revenues — of 200 oil and gas facilities. We have disrupted its command structure, undermined its propaganda, taken out half of its senior leadership, squeezed its financing, damaged its supply networks and dispersed its personnel.

Consider the case of Kobani, on Syria’s border with Turkey, which was threatened with annihilation after Islamic State captured more than 300 nearby Kurdish villages. The militants already controlled large swaths of the city itself, and both they and the world’s media expected an easy victory. But thanks to diplomatic cooperation among coalition partners, targeted air strikes and on-the-ground support from Iraqi Kurdish forces, the militants were driven out, after losing roughly a thousand fighters.

But defeating Islamic State is only the beginning. The fight against violent extremists will not be decided on the battlefield alone. It will be decided in classrooms, workplaces, houses of worship, community centers, urban street corners, and halls of government. And it will be decided by the success of our efforts to stop terrorist recruitment; address the intolerance, economic hopelessness and exclusion that help create vacuums which extremism fills; and create credible, visible and empowering alternatives to violent extremism in countries where it is prevalent.

In recent years, it has been fashionable to look at challenges like these and pontificate that the international system is somehow unraveling.

I strongly disagree. In fact, I see the opposite. I see countries working together to negotiate new and far-reaching trade pacts, covering some 70 percent of global GDP.

I see the world working together to end the Ebola pandemic. I see work to achieve a peaceful resolution to the threat posed by Iran’s nuclear program. I see cooperation to reach an ambitious global agreement on climate change, and to curb the strife in places like the Central African Republic, Colombia, and the Democratic Republic of Congo.

Yes, these are challenging times. But I see countries around the world reducing extreme poverty, improving maternal health care, aiding child nutrition, expanding access to primary education, and increasing life expectancy.

More people have attained — or are reaching for — prosperity than at any time in history, and, despite the threat that violent extremism poses, the percentage of people who die violently has reached a low for the modern era. All of this has happened or is happening because of the strength of the international order. We just need to help bring that reality to the places where today it feels a million miles away.

We are fortunate to be the descendants of innovators, of doers, of people who overcame slavery, plagues, depressions, global wars and totalitarianism — people who were utterly unafraid of great challenges and were most effective when put to the test.

Now it is our turn. The tests that we face today compel us to prepare and to plan, to unite and to defend our collective future from the atavistic paranoia of terrorists and thugs. The future still belongs to the universal values of civility, reason and the rule of law.

John F. Kerry, a former U.S. senator from Massachusetts, is U.S. secretary of state. This commentary was adapted from a speech delivered at this year’s Munich Security Conference. © 2015 Project Syndicate (www.project-syndicate.org)