WASHINGTON – American leadership is the one constant in an uncertain world. As Americans, we see the future not as something beyond our control, but as something we can shape for the better through concerted and collective effort. That was true this week, as we mobilized the world to confront some of our most urgent challenges.

America is leading the world in the fight to degrade and ultimately destroy the terrorist group known as the Islamic State. This group has terrorized all who they come across in Iraq and Syria. In the most horrific crimes imaginable, innocent human beings have been beheaded, with videos of the atrocity distributed to shock the conscience of the world. There can be no reason, no negotiation, with this brand of evil. The only language understood by killers like this is the language of force.

In this effort, we do not act alone. Nor do we intend to send American troops to occupy foreign lands. Instead, we will support Iraqis and Syrians fighting to reclaim their communities. We will use our military might in a campaign of airstrikes to roll back the Islamic State, and we will be joined by friends and partners, including Arab nations. We will train and equip forces fighting against these terrorists on the ground. We will work to cut off their financing, and to stop the flow of fighters into and out of the region. Already over 40 nations have offered to join the coalition against the Islamic State, and at the United Nations in New York, I worked to build more support for this coalition.

In my annual address to the U.N., I also challenged the world — especially Muslim communities — to explicitly, forcefully and consistently reject the ideology of al-Qaida and the Islamic State. No children, anywhere, should be educated to hate other people. We must cut off the funding that fuels violent hatred, and contest the space that terrorists occupy, including the Internet and social media. At the same time, countries must do more to offer an alternative vision, and to tap the extraordinary potential of their young people.

American leadership is not confined to the fight against the Islamic State. We are leading the effort to rally the world against Russian aggression in Ukraine. Along with our allies, we will support the people of Ukraine as they develop their democracy and economy. We will reinforce our NATO allies, and uphold our commitment to collective defense. We will impose a cost on Russia for aggression, and counter falsehoods with the truth. And this week, I called upon even more nations to join us on the right side of history.

America is leading the fight to contain and combat the Ebola epidemic in West Africa. We’re deploying our doctors and scientists – supported by our military – to help fight the outbreak and pursue new treatments. From the United Kingdom and Germany to Senegal and France, other nations are stepping up their efforts, too, by sending money, supplies and personnel. But we need an even broader effort to stop a disease that could kill hundreds of thousands, inflict horrific suffering, destabilize economies and ultimately spread across borders. That’s why we will continue to rally other countries to join us in making concrete commitments to fight this disease, and enhance global health security for the long term.

America is engaging more allies and partners to confront the growing threat of climate change before it’s too late. At home, we’ve taken historic steps to invest in clean energy, cut carbon pollution and create new jobs in the process. Abroad, our climate assistance now reaches more than 120 nations. But we can only succeed in combating climate change if we are joined in this effort by every major power. So on Tuesday, I called on every nation – developed and developing alike – to join us in this effort for the sake of future generations.

America will do what it takes to meet the tests of this moment. Because despite all the challenges of this new century, there is no nation on Earth better positioned to seize the future than ours. The people of the world still look to us to lead. And we welcome that responsibility. We are heirs to a proud legacy of freedom, and as we showed the world this week, we are prepared to do what is necessary to secure that legacy for generations to come.