The U.S. has been at war for more than 20 of the past 25 years in three major conflicts all in the same region. First, Afghanistan, then Iraq, now Iran.

U.S. presidents said overwhelming American miliary firepower would decide all these wars swiftly. Under President George W. Bush, the U.S. military needed just weeks to oust the Taliban in Afghanistan in 2001 and President Saddam Hussein in Iraq in 2003. Under President Trump, the U.S. bombing campaign, assisted by Israel, killed many of Iran’s leaders on the first day of the war and hammered the country at will.

Yet time and again, raw military might has not translated into clear political success and the kind of fundamental change the U.S. has sought. Today, the Taliban are running Afghanistan. Iraq has achieved a measure of stability, but still struggles on many fronts after a long, brutal war. Iran’s theocratic regime remains in place, the war still unresolved.

Why is the U.S. finding it so hard to win wars?

“We generally do a pretty good job of the breaking things and killing people at the inception of the wars,” said Peter Bergen. He’s the author of a new book, All The Presidents’ Wars, which looks at U.S. conflicts over the past quarter-century. Bergen, a national security analyst at CNN, said the U.S. keeps falling short when it comes to ending wars.

“We, the United States, tend to not plan for the day after — the peace that follows the war,” said Bergen.

A reliance on military power over diplomacy

With an emphasis on military power over diplomatic deals, the U.S. keeps expecting wars that can be wrapped up quickly and at a relatively low cost, said Paul Salem, a Middle East analyst in Lebanon.

“The U.S. has an imperial appetite, but a tourist’s approach to it,” said Salem, who’s with the Center for Strategic and International Studies, a Washington think tank. He said this contradiction defined the conflicts in Iraq and Afghanistan and a similar scenario is playing out in Iran.

“Their recent history is not one of stability and deep institutions that you can just come in and change somebody at the top and everything works out,” said Salem.

Bergen offers a similar assessment. He said the U.S. has been acting like an empire without wanting to be an empire.

“Empires typically require people to learn languages, stay there for a long time, not be there on just short tours,” Bergen said. “We don’t do the kinds of things that would be necessary to hold on to territories for a long time. We’re very reluctant to do it.”

Trump reverses a campaign promise

Trump pledged to keep the U.S. out of “forever wars.” Yet in attacking Iran, he’s taking on the largest and most powerful U.S. rival in the region. And the president is trying to do it without ground troops, which has limited U.S. casualties compared to the earlier wars.

Douglas Lute, a retired Army lieutenant general, is a critic of the Iran war and does not support using ground troops. But he said it’s important to recognize that without them, the U.S. needs to scale back its goals.

“When we launch only a bombing campaign but we retain maximalist goals, like regime change, you don’t have any prospect for success unless you’re just lucky. And being lucky is not the place to start a military campaign,” said Lute.

At various times, Trump has called for eliminating Iran’s nuclear program, toppling the government, destroying its air force, navy and missile program. Lute sees parallels to earlier wars when he served as the so-called “war czar,” coordinating efforts in both Iraq and Afghanistan under presidents Bush and Obama.

“We’ve had repeated disconnects between ends, ways, and means. We’ve had a lack of sufficient understanding of what we were getting into,” said Lute, who also served as the U.S. ambassador to NATO.

The challenge of asymmetric warfare

For all its muscle, U.S. military power has its limits, and groups fighting on their home turf have found ways to hobble the American military, even if they can’t match its firepower.

In Afghanistan and Iraq, militants turned to roadside explosives and suicide bombers to keep U.S. forces off balance. In Iran, the military there has turned to low-cost drones and has effectively shut down the Strait of Hormuz even though the U.S. has decimated Iran’s traditional navy.

“Those dazzled by the technological wizardry of an F-35 or the ability of the United States, Israel, and a few others to conduct complicated combined arms operations have failed to recognize that warfare has been slowly shifting in favor of local defenders, even when facing seemingly superior foes,” Harvard professor Stephen Walt wrote recently in Foreign Policy.

“The United States had command of the air, the ability to survey complex battle spaces in real time, and overwhelming superiority in firepower in both Iraq and Afghanistan,” he added.

The U.S. often believed it could eventually defeat these weaker foes, and has been reluctant to turn to diplomacy, according to Salem.

“Advice from the State Department was kind of brushed aside as too weak and too wimpy,” said Salem. “We’ve seen it again in this [Iran] war. There’s barely any State Department input or advice.”

The Middle East war that went well

These analysts said there is a Middle East war that offers valuable lessons — the first U.S. war against Iraq in 1991. The goal was limited to driving out the Iraqi troops who’d seized Kuwait.

President George H.W. Bush rallied support at the United Nations and built a large international force before launching the war.

“I count that war as the last time that we really had realistic objectives,” said Douglas Lute.

At that time, he was an Army major in a cavalry unit. The U.S. bombed Iraqi forces for five weeks, then unleashed a swift, decisive ground campaign that lasted just four days before the Iraqi troops fled Kuwait.

“We had admittedly limited objectives, which was to liberate Kuwait,” said Lute. “It was not to take on Baghdad, not to overthrow Saddam [Hussein], not to replace the Iraqi government.”

Trump is looking to end the Iran war. Yet Paul Salem thinks that however this conflict concludes, it won’t be the final word. The U.S., he said, is capable of striking Iran whenever it wishes.

While Iran will be vulnerable, “it is able to inflict a cost on the global economy and, indirectly, on the U.S. president. I think there will be future wars and confrontations,” Salem said.

And it’s still not clear how the current one will end.