It is the modern era's military strategy of choice: overwhelming air power delivering precision-guided punishment backed by intelligence on the ground, with minimal exposure for soldiers of the striking side.

Seductive though it is to risk-averse governments with war-weary publics, the approach has its limits — and these are on display in Syria and Iraq, where a U.S.-led coalition has carried out over 4,100 airstrikes against Islamic State radicals yet failed to stop the extremists.

August will mark a year since the campaign was launched after tens of thousands of minority Yazidis were forced to flee an onslaught by the militants in Iraq, causing a humanitarian crisis.

It was clear from the start that a ground force was needed, and Iraqi and Syrian Kurdish fighters have had successes on the battlefield. The Iraqi military was also to play a key role: air power would soften up the extremists, weakening them or getting them to flee, and the Iraqis were to deliver the final blow or retake areas abandoned by the militants.

That has not gone according to plan.

Badly humiliated and Shiite-dominated, Iraq's army has shown little stamina in the mostly-Sunni cities taken by the Islamic State militants. In recent days U.S. Defense Secretary Ash Carter assessed it lacked the "will to fight" after fleeing Ramadi, the strategic capital of Iraq's largest Sunni province, Anbar, leaving the Islamic State group in control of nearly all its territory, which stretches to the Jordan border.

Overall the extremists remain in control of about a third of Iraq and Syria, equivalent to the amount of territory under its authority before the air campaign began. It continues to terrorize the population there, imposing its unforgiving brand of radical Islam and terrorizing minority groups in shocking fashion, including sexual enslavement of women.

It has suffered some setbacks and also made some gains. The checklist appears to point to a tie — with advantage, Islamic State:

— The group has held on to its main hubs in Iraq and Syria, Mosul and Raqqa, as well as Fallujah, a strategic Iraqi town a short drive from Baghdad.

— It is battling to a tie around Beiji, home to Iraq's major oil refinery that has yet to fall but is surrounded. Iraqi security forces have poured resources and manpower into securing the refinery, and the militants stage periodic attacks on the complex.

— In Syria it was rebuffed by a massive air campaign in the Kurdish town of Kobani on the Turkish border, but in recent days, its fighters have captured the Syrian town of Palmyra, the site of 2,000-year-old Roman ruins. That has brought it closer to Damascus.

There are success stories — most recently in Saddam Hussein's hometown of Tikrit, where 11th-hour U.S. airstrikes proved to be a game-changer after a large-scale Iraqi operation to retake the city stumbled.

While air power has proven well-suited to hitting command-and-control centers, storage facilities and infrastructure, Islamic State fighters have proven adept at reacting. The group "is nimble enough to move around their personnel and equipment to make up for any losses with tactical moves," said Dubai-based geopolitical analyst Theodore Karasik. "The battlefield is very fluid."

At a meeting of top Arab officials and business people sponsored by the World Economic Forum in Jordan last weekend, there was a strong sense that the coalition must reassess if it hoped to a avoid a protracted conflict, or some other version of failure.

Some yearned for a return of the U.S. military, although none would say so on the record. After the grim experience for Americans in Afghanistan and Iraq since 2001, with thousands of U.S. lives lost and billions of dollars squandered, it simply wouldn't fly.

All seemed to agree that a rethink was in order. But for now, the Obama administration remains opposed to sending U.S. forces back into combat in Iraq and is calling for patience and time to train Iraqis. Perhaps in the long run, a new pan-Arab strike force being promoted by Egypt might be the answer.

As unhappiness mounts with coalition performance, here are some issues to consider:

YEMEN

Another air campaign carried out by a coalition of Sunni Arab nations led by Saudi Arabia has had similarly disappointing results, this time against Shiite Houthi rebels who seized much of Yemen, including the capital, Sanaa. After two months of airstrikes, the Houthis have been damaged, but they haven't been expelled from any major areas they control.

Like Islamic State, the Houthis and their allies have devised tactics to avoid being hit from the air, using public transportation and motorcycles to deploy forces or traveling at night on foot or in vehicles with their headlights dimmed. And like the jihadis, they easily melt into urban civilian areas under their control — practically daring coalition forces to try to bomb them out. As long as the rebels control the local population and have little concern for the suffering of civilians, this can create pressure on the attacking side, which soon stands accused of humanitarian abuses.

By contrast, airstrikes did succeed for Israel in stopping Hamas rocket fire from Gaza last summer, and for NATO in 1999 in getting Serbia to eventually relinquish Kosovo. But this was against state actors that ultimately felt beholden to their suffering populations.

NO ALLY IN SYRIA

Whereas in Iraq the coalition has a weak ally, in Syria it is hampered by having no real ally at all. Indeed, it has going out of its way to avoid the impression of working with the government of Bashar Assad, who many around the world see as having lost any legitimacy to rule.

Despite calls by antiquities officials to help save Palmyra this week, the coalition refrained from interfering, launching one airstrike that struck only after the town had already fallen and Syrian government troops defending the town had fled.

Instead, the U.S.-led coalition is working mainly in support of Syria's Kurds, launching daily airstrikes that concentrate on areas around Kobani and the predominantly Kurdish province of Hassakeh in the northeast. Kurdish fighters, supported by air cover from the coalition, have made significant advances, taking back dozens of villages in recent days.

THE PSYCHOLOGICAL EDGE

In any fight, it is the fearless side that usually enjoys the edge. Unlike Western troops, jihadis like the Islamic State group seem unafraid to die in airstrikes and pleased to dispatch suicide attackers who are difficult to stop. Facing a declared offensive by the Iraqi army in Anbar province this week, the militants did just that, unleashing a wave of suicide car bombings that killed at least 17 troops, including a top commander.

It is part of the group's psychological warfare: A seemingly inexhaustible supply of willing bombers at the wheel of trucks loaded with explosives. High-definition propaganda videos follow, showing the trucks speeding toward their target before exploding into fire and clouds of black smoke, devastating Iraqi forces' morale.

The U.S. has promised to deliver more anti-tank weapons to counter the suicide bombers. But in an almost comical indication of the futility, the U.S. has had to devote some of its airstrikes to destroying tanks and other U.S.-supplied weaponry that the Iraqis have abandoned to the Islamic State fighters.

___

Perry reported from Cairo. AP writers Jon Gambrell and Hamza Hendawi in Cairo, Zeina Karam in Beirut and Adam Schreck in Dubai contributed to this report.

___

Dan Perry is AP's Middle East editor leading text coverage in the region. Follow him on Twitter at www.twitter.com/perry_dan

Vivian Salama is the Associated Press bureau chief in Baghdad. Follow her on Twitter at www.twitter.com/vmsalama.