For a few months, the marauding jihadis of ISIS might have looked like an unstoppable army. That’s when they were moving at high speeds, their power blurred by hype and velocity. Slowed down by real resistance, a clearer picture takes shape and the limits of ISIS’s military power come into focus.

At the so-called caliphate’s edges, in areas like the Syrian border town of Kobani, ISIS’s march has stalled and its armor is starting to crack. We may be reaching the limits of ISIS as a conventional military force.

Facing a small Kurdish resistance and Western airpower, ISIS has been unable to take Kobani, despite surrounding and besieging it for months. That doesn’t mean the group is giving up, though, or anywhere close to defeat. The façade of ISIS’s power as a conquering army may be wearing off, but they can still revert to terrorist form and continue killing even if they can’t take ground.

Early on, ISIS leaders committed to a risky gambit: They decided to form a state, which put them in open conflict with other world powers. The group could have survived as a terrorist organization or a local insurgency as it had for years, but instead wagered on the caliphate. That decision provided an aura of authority that attracted new recruits and seemed to pay off in the short term. But it also transformed a regional threat into a global enemy that was easier to target in the areas it controlled.

Since then ISIS had acted as part state, part Taliban-style insurgency, and part al Qaeda-style jihadi terrorist group.

Despite the pathological absolutism of ISIS’s beliefs, it has proved flexible on the battlefield. As the tactics that won ISIS its most stunning early victories become harder to pull off in the face of warplanes and fierce local resistance, the group has adapted.

Lauren Squires, a research analyst at the Institute for the Study of War and former Army intelligence analyst, attributes ISIS’s successes to “their ability to conduct hybridized warfare—part conventional war and part terrorist guerrilla campaign.” Air power may blunt ISIS’s momentum, Squires said, but “it will only be in the near term, they will adapt to using the guerrilla side of the spectrum.”

Depending on the enemy it faces, and its own vulnerabilities, ISIS moves along the state-terrorist spectrum of power. Blending into the local population in one area to operate in the shadows, while marching openly through the streets elsewhere. In battle, it means the ability to shift from suicide bombers to tank columns and maneuver warfare in the span of a day.

The transition to statehood started with the June campaign that captured Iraq’s second largest city, Mosul, and put the jihadi army’s strengths on display. It showed effective planning that used a sustained preliminary attack to weaken the enemy before a blitz assault; good command and control over a large force combined with autonomy and initiative from small unit leaders; and the rapid repositioning of forces to seize new opportunities and maintain the element of surprise. All of those qualities together allowed an ISIS army of fewer than 10,000 to rout the better armed Iraqi Security Forces that numbered near 30,000.

But even in June it was clear that ISIS’s victories weren’t due to military prowess alone. The offensive that toppled Mosul also depended on another key factor: the will to fight. The ISIS attackers believed their own hype and were willing to die fighting while the mainly Shia security forces, led by corrupt commanders who weren’t ready to be killed defending Sunni areas far from their homes.

Iraq analyst Michael Knights conducted a thorough study of ISIS’s military abilities in late August for West Point’s Combatting Terrorism Center and concluded that ISIS “is a military power mostly because of the weakness and unpreparedness of its enemies.”

Some of that weakness was instilled by ISIS’s own actions. Months of targeted killings had wounded and demoralized the security forces in Iraq’s north before ISIS fighters moved en masse to finish them off. What resistance ISIS couldn’t assassinate it instead tried to break psychologically. In a propaganda campaign that swarmed social media with images of death and dismemberment, ISIS terrorized its enemies, warning that the same gruesome fate awaited them if they didn’t flee.

At the same time, the gorier the propaganda, the better it was for ISIS recruiting. Gulf state fundamentalists, battle-hardened Chechens, and middle-class Londoners were all drawn into ISIS by its powerful messaging and the promise to, in a twist on an old phrase, be the evil you want to see in the world.

ISIS chose its early targets carefully. Mosul was the culmination of a long, deliberate strategy. It’s also a city with a Sunni majority where ISIS could count on winning some local support.

Driving outward, to enlarge the borders of its state, ISIS can’t be as selective anymore about the enemies it encounters. Nor can it count on local support in areas outside of the Sunni belts or an opposition primed to surrender by its ghoulish propaganda.

While ISIS’s videos of mass murder and murder-scene tweets once scared off its enemies, that approach is now having the opposite effect. Non-Sunni foes of ISIS, such as the Kurds in Kobani, believe they’ll be slaughtered even if they surrender—ISIS’s own publicity has convinced them of it—so they’re steeled for an all-or-nothing fight.

Before Kobani, the same logic had played out in other battles. The Shia town of Amerli managed to fend off ISIS attacks for months before American air power allowed the Iraqi army and Shia milita groups to break the siege.

While Mosul showed what ISIS was capable of against a weakened enemy, the Kurdish town of Kobani is proving the limits of ISIS’s ability against a determined resistance.

Even before U.S. cargo planes dropped weapons and other critical supplies into Kobani on Sunday, the YPG, a Kurdish resistance group, had held off surrounding ISIS fighters for months. ISIS has penetrated into the city and launched attacks from three fronts but the Kurdish forces have so far held up their defense and kept Kobani from falling.

Now, with the YPG resupplied and airstrikes against ISIS targets around Kobani intensifying, ISIS may be facing its first major loss. Unable to break through Kobani’s defenses Monday, ISIS launched a series of attacks against Kurdish targets in both Syria and Iraq.

If ISIS can’t break Kobani through a conventional military assault, the group can always revert to terrorist form. On Monday in Baghdad—another city ISIS has been attacking for months with far less chances of capturing—a suicide bomber killed 17 people.

Without an opposing ground force capable of defeating them, air power may push ISIS back from Kobani’s walls, but that won’t stop its attacks. It’ll adapt again and survive as it has for more than a decade.