Samantha Power, the U.S. Ambassador to the United Nations, warned the American public against a kind of intervention fatigue, emphasizing that U.S. leadership is needed now more than ever amid global threats from Ebola to the Islamic State.

“I think there is too much of, ‘Oh, look, this is what intervention has wrought’ … one has to be careful about overdrawing lessons,” Power said Wednesday during the Defense One Summit. At the same time, she said, “we are asking an awful lot right now of our forces.”

“The risk of using military force is so significant … there should be a lot of layers and a lot of checks and balances. But at the same time there are really profound risks to our national security that exist today.”

Power just returned from West Africa, where she met members of the U.S. military who are providing crucial tactical support for Operation United Assistance to help stop the spread of Ebola. Power is reporting her temperature twice a day, and is nearing the end of the 21-day monitoring cycle.

Power described her trip as an example of the unique capabilities of the U.S. and its military.

Yet a slew of recent threats, from Russia to China and beyond, also highlight the deep divide in the American public and its politics over when to intervene across the globe.

The U.S. intervention in Libya in 2011 has become a case study for intervention

It was a model in terms of the coalition the U.S. built, she said, but “the challenge is that there is in Libya a set of tribal dynamics that were unleashed.”

While she cautioned against comparing interventions, she drew some parallels between the Libya intervention and the military operation against the Islamic State, which expanded from Iraq into Syria.

“The moderate opposition in recent months has lost ground, no question,” she said. U.S. military strikes in Syria have been limited in their effectiveness at degrading the Islamic State, and according to some reports, have benefitted Syrian President Bashir al-Assad. But Power emphasized that there remain Syrian rebels who “still espouse the vision for Syria that drove the revolution in the first place.”

The Obama administration is preparing to vet, train and equip moderate Syrian opposition. “We hope to be getting that off the ground as quickly as possible so that they can get some relief from that two-front war … and better approach the Syrian regime,” she said.

Given the risks of using U.S. force abroad, she said she understands a healthy dose of skepticism. The American public—particularly its representatives in Congress—are rightfully wary of what she called the “free rider problem,” because “too often the United States ends up carrying the lion’s share of the humanitarian effort.

At the same time, she said, the American people can be trusted to understand that the international peace keeping efforts that the U.S. significantly supports are inextricable from our national security interests.

The Islamic State is “a terrorist movement that’s the first of its kind,” she said. “That is the kind of terrorism juggernaut that the American people understood we couldn’t tolerate.”