ARLINGTON, Va. — Defense Secretary James Mattis said the long-awaited review of U.S. policy in Afghanistan “just takes time” and “is hard work,” so the Pentagon is “working to get it right.”

“If you go back and you look at why did we win World War II, and then you look at what happened in Korea — by the way, we’re still at war, armistice, no peace treaty. Vietnam, you know how that went. You move forward, Iraq and what happened there,” Mattis told reporters today. “If you don’t get the big ideas right, and this is not easy. I’ve done tactics. I’ve done operations. I’ve done strategy. Strategy is orders of magnitude more difficult.”

“It’s easy only for the people who criticize it from the outside and don’t carry the responsibility for integrating it all together, diplomatic, economic, long-term views, short-term urgencies, that sort of thing,” he added. “And so, as you put it together, it just takes time. It just takes time.”

“It wasn’t that past presidents were somehow dumb or anything else.”

Still, he promised that the department is “close” to finishing the assessment of U.S. involvement in the 16-year war.

“We know there will be some allies who are willing to do — to send more troops. We’re aware of that. But again, their troops are as precious to them as ours are to us. We’ve got to get this thing right,” Mattis said.

Asked how many troops the U.S. might be committing to Afghanistan in future, the Defense secretary replied, “I don’t know if I want to tell the enemy that. We may be able to, depending on what it will reveal. If it’s a gross number and they don’t know, for example where we’re sending them or something, there may be a way to do it.”

“I’m always going to be conservative,” he added. “If it’s going to endanger the troops, nope, not going to talk about it.”

Mattis said he thinks ISIS leader Abu Bakr al-Baghdadi is still alive, “and I’ll believe otherwise when we know we’ve killed him.” The Pentagon has discounted earlier claims from Russia and Iran that the self-proclaimed caliph had been killed.

“For obvious reasons, we’re trying to track him pretty closely because he’s declared war on us. So, he’s going to reap his reward for it, you know?” he said. “I think he’s alive. And that means he would be — have a role to play, obviously, in the organization that he leads. To define that role, is it operational, is it strategic, is it propaganda, is it spiritual, is it physical? I can’t define it. But until I see his body, I’m going to assume he’s alive.”

Mattis laughed when he was asked if he’d like to shoot down one of North Korea’s test missiles.

“I can just read the headlines,” he said. “I ain’t going to answer that one.”