WASHINGTON — With alarming frequency in recent years, thousands of American-trained security forces in the Middle East, North Africa and South Asia have collapsed, stalled or defected, calling into question the effectiveness of the tens of billions of dollars spent by the United States on foreign military training programs, as well as a central tenet of the Obama administration’s approach to combating insurgencies.

The setbacks have been most pronounced in three countries that present the administration with some of its biggest challenges. The Pentagon-trained army and police in Iraq’s Anbar Province, the heartland of the Islamic State militant group, have barely engaged its forces, while several thousand American-backed government forces and militiamen inAfghanistan’s Kunduz Province were forced to retreat last week when attacked by several hundred Taliban fighters. And in Syria, a $500 million Defense Department program to train local rebels to fight the Islamic State has produced only a handful of soldiers.

A United States Army trainer instructed Iraqi recruits in Taji in April. Many Iraqi soldiers have joined the exodus of migrants to Europe. CreditJohn Moore/Getty Images

American-trained forces face different problems in each place, some of which are out of the United States’ control. But what many of them have in common, American military and counterterrorism officials say, is poor leadership, a lack of will and the need to function in the face of intractable political problems with little support. Without their American advisers, many local forces have repeatedly shown an inability to fight.

“Our track record at building security forces over the past 15 years is miserable,” said Karl W. Eikenberry, a former military commander and United States ambassador in Afghanistan.

The American military has trained soldiers in scores of countries for decades. But after the terrorist attacks of Sept. 11, 2001, that mission jumped in ambition and scale, especially in Afghanistan and Iraq, where the ultimate goal was to replace the large American armies deployed there.

The push to rebuild the Iraqi Army that the United States disbanded after the 2003 invasion had largely succeeded by the time American troops withdrew eight years later. But that $25 billion effort quickly crumbled after the Americans left, when the politicization of the army leadership under Prime Minister Nuri Kamal al-Maliki eroded the military’s effectiveness at all levels, American officials said.

In Afghanistan, basic training typically included marksmanship, ambush drills and other counterterrorism skills. Before they could begin that, most new Afghan recruits also needed time-consuming literacy training so they could read the serial numbers on their weapons, or lessons on proper hygiene to prevent illnesses that would reduce their effectiveness in combat. Still, there were notable successes: Afghan special forces trained and advised by their American counterparts proved to be especially capable fighters.

Then, in a commencement speech at West Point in May 2014, President Obama put the training of foreign troops at the center of his strategy for combating militant groups that threaten American interests. The United States, he said, will no longer send large armies to fight those wars and, in the case of Afghanistan, would continue to withdraw the forces that are there. Instead, it will send small numbers of military trainers and advisers to help local forces, providing them with logistical, intelligence and other support.

“We have to develop a strategy,” Mr. Obama said, “that expands our reach without sending forces that stretch our military too thin or stir up local resentments. We need partners to fight terrorists alongside us.”

Expensive Failures

Mr. Obama’s approach has already endured several setbacks, but with no political appetite among most Republicans or Democrats to send in large numbers of American troops, the administration is adjusting its strategy, often turning to regional allies for help in supporting local forces.

In northwest Africa, the United States has spent more than $600 million to combat Islamist militancy, with training programs stretching from Morocco to Chad. American officials once heralded Mali’s military as an exemplary partner. But in 2012, battle-hardened Islamist fighters returned from combat in Libya to rout the military, including units trained by United States Special Forces. That defeat, followed by a coup led by an American-trained officer, Capt. Amadou Haya Sanogo, astounded and embarrassed American commanders. French, United Nations and European Union forces now carry out training and security missions in Mali.

In Yemen, American-trained troops and counterterrorism forces largely disbanded when Houthi rebels overran the capital last year and forced the government into exile. The United States is now relying largely on a Saudi-led air campaign that has caused more than 1,000 civilian casualties.

More recently in Afghanistan, Iraq and Syria, the military campaigns against the Taliban and the Islamic State, also known as ISIS or ISIL, have made little headway. After acknowledging that only four or five American-trained Syrian rebels were actually in the fight there, Pentagon officials said last week that they were suspending the movement of new recruits from Syria to Turkey and Jordan for training. The program suffered from a shortage of recruits willing to fight the Islamic State instead of the army of President Bashar al-Assad, a problem Mr. Obama noted at a news conference on Friday.

“I’m the first one to acknowledge it has not worked the way it was supposed to,” he said. “A part of the reason, frankly, is because when we tried to get them to just focus on ISIL, the response we get back is, ‘How can we focus on ISIL when, every single day, we’re having barrel bombs and attacks from the regime?’ ”

In Afghanistan, the United States has spent about $65 billion to build the army and police forces. Even before last week’s setback in Kunduz, many Afghan forces were struggling to defeat the Taliban, partly because of what many senior commanders said had been a precipitous American drawdown before Afghans were ready to be on their own. But how thousands of Afghan Army, police and militia defenders could fare so poorly against a Taliban force that most local and military officials put only in the hundreds baffled and frustrated the Pentagon.

If there is a bright spot in the training landscape, it may be the American-financed effort by a 22,000-member African Union force — from nations like Kenya, Uganda and Ethiopia — to oust the Shabab, Al Qaeda’s affiliate in Somalia, from many areas of the country. The Shabab’s leader, Ahmed Abdi Godane, was killed last year in an American airstrike, and other agents have been killed by drone strikes.

The American government has invested nearly $1 billion in the overall strategy in Somalia. But even with the gains, the Shabab have been able to carry out bombings in Mogadishu, the capital, and in neighboring countries, including massacres at a university and a shopping mall in Kenya in the past two years.

Shiites Step Back

Much more complicated is the situation in Iraq. A United States training program to strengthen the embattled security forces there has run aground, in part because the Iraqi government has provided far fewer recruits than anticipated, while many Shiite militiamen and soldiers who were fighting the Islamic State have left the battlefield and joined the exodus of migrants seeking new lives in Europe.

The reality is that Iraq’s Shiite majority seems to be settling in to a divided Iraq and increasingly questioning whether it is worth shedding Shiite blood in areas like Anbar Province or Mosul, Iraq’s second-largest city, which the Islamic State captured in June 2014. The battle against the Islamic State is no longer the national priority it was a year ago, when the militantsthreatened Baghdad and the Shiite-majority south.

With those areas now largely secure, mostly because of the efforts of Iranian military advisers and their proxy militias, the Iraqi government is focused on other priorities — mostly the migrant crisis and street protests, which led to a series of proposals by Prime Minister Haider al-Abadi.

For the White House, which hoped to rely on a rehabilitated Iraqi Army and Shiite militias to fight the Islamic State, this raises troubling questions and highlights the diverging interests of the United States and its partner.

Vali Nasr, dean of the School of Advanced International Studies at Johns Hopkins University and a former senior adviser at the State Department, said there was a deepening sense in Iraq that “ISIS is a Sunni problem, not a Shia problem.” He said the prevailing belief now among Shiites was that saving Anbar was not worth “the blood of our children.”

Maps have even circulated that show the territory the Shiite militias and their sponsors in Iran care about. A line stretches from the Iranian border in the east to just south of Kirkuk; around Samarra and to the edge of Baghdad; and then across Anbar, south of Falluja, toward the Jordanian border.

Sajad Jiyad, an Iraqi analyst based in London and Baghdad who has advised the Iraqi Defense Ministry, saw one of the maps and described it as “the lines they are not willing to concede.”

This is a significant shift. Last summer, during the Islamic State’s onslaught into Iraq, tens of thousands of Shiite men took up arms after Grand Ayatollah Ali al-Sistani, the spiritual leader for Iraqi Shiites, issued a fatwa. As recently as four months ago, after Ramadi, the capital of Anbar,fell to the Islamic State, militiamen streamed into the province, promising to quickly drive the militants away.

American officials had long worried that the militias, the most powerful of which are supported by Iran, would be counterproductive if they fought in Sunni areas, because they could exacerbate sectarian tensions.

But in Anbar, the situation was so dire that local Sunni officials invited the militias in, and the Americans largely acquiesced as long as the groups coordinated with the Iraqi government so that American warplanes would not mistakenly bomb them. Now, more than four months after the fall of Ramadi, despite American and Iraqi officials’ promises of a robust counteroffensive, the fight has come to a stalemate.

And many of the Sunnis who sought help from the militias now regret it. Several officials said that instead of helping liberate Anbar from the Islamic State, the Shiite militias had settled into relatively safe areas of the province, raising fears that their goal — and that of their sponsor, Iran — is to set up a permanent presence there as part of a plan to protect Baghdad and the south.

Sheikh Rafi al-Fahdawi, a Sunni tribal leader in Anbar, said the militia fighters had “isolated themselves in certain areas and don’t want to participate in the important battles.”

The United States and 16 allied countries have so far trained six Iraqi Army brigades and 10 Kurdish pesh merga battalions, or about 12,000 troops, according to the Defense Department. About half of the army troops are now in the fight, with the others training on their equipment and soon to follow, American military officials said.

One option now for the United States is to emphasize training and equipping Sunni tribal fighters, something the Obama administration has long sought to do. But while there are about 5,600 Sunni fighters in Anbar as part of the Popular Mobilization Forces, the umbrella group for the largely Shiite paramilitary forces, they have yet to prove themselves in combat.

An Iraqi official briefed on the military situation in Anbar, who spoke on the condition of anonymity because he was not authorized to talk to the news media, said, “I don’t think there is a sense of urgency anymore.”

“Clearly, there is no progress,” the official said. “Why there is no progress is what everyone is talking about. I don’t think there is any will among the Iraqi security forces and militias to fight. They are just not fighting.”

Soldiers and militiamen, many of whom said they had not been paid in months, are dropping their weapons and heading for Europe.

One militia fighter from Diyala Province, who refused to give his name because he had abandoned his unit, spoke recently from Germany. “I almost got killed more than five times because we went into highly dangerous areas,” he said. “I considered moving to Europe as the last option for me to live in a country away from the hissing of bullets and death.”

John E. McLaughlin, a former deputy director of the C.I.A. who is now at the Johns Hopkins School of Advanced International Studies, said American efforts to train the Iraqi military would probably be futile without a political bargain to unite the country’s Shiite and Sunni Arabs.

“Training is a necessary but not sufficient way to get you to the point of creating a robust fighting force, because ultimately, militaries fight over political issues,” he said.