ISIS: Slow, Long fight : airstrikes, failures on ground.

(CNN) -- Not weeks. Not months. Years.

That's how long nations entering the fight against ISIS may need to be prepared to spend on the battle, British and U.S. officials say.

British Prime Minister David Cameron told Parliament Friday of the likely length of the mission ahead of what turned out to be an overwhelming vote to send UK air power into the fight.

But, he said, what choice does the country have when faced with a well-funded, highly organized force known for virtually unmatched cruelty?

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"Beheadings, crucifixions, the gouging out of eyes, the use of rape as a weapon, the slaughter of children. All these things belong to the Dark Ages," Cameron told British lawmakers.

"Left unchecked, we will face a terrorist caliphate on the shores of the Mediterranean and bordering a NATO member, with a declared and proven determination to attack our country and our people," he said.

The same message came from the Pentagon Thursday: It's going to take years.

"We are steeling ourselves for that period of time," spokesman Rear Adm. John Kirby said.

Coalition grows

In addition to Great Britain, Denmark also agreed Friday to join the list of more than 50 countries that have agreed to support the fight against ISIS.

Demmark will send seven F-16 fighter jets, a spokeswoman said.

On Friday, Russian Foreign Minister Sergey Lavrov also offered to support Iraq in fighting terrorists, "above all the Islamic State."

The new support came amid fresh battles between Kurdish Syrian fighters and ISIS militants near a city on the border with Turkey.

CNN's Phil Black, watching the fighting from a hillside in Turkey, reported hearing small arms and artillery fire as the Kurdish and ISIS forces fought to advance toward the Syrian city of Ayn al-Arab.

Turkish Kurds gathered near the border to watch the fighting cheered whenever ISIS fighters appeared to take a hit.

A resident of the city, also known as Kobani, told CNN that ISIS forces are 2 kilometers (1.24 miles) from the city and that resistance forces are running low on ammunition.

"We are hoping and waiting for any coalition air strike on these terrorists, to save our city from the barbaric attack," Hussein Kamal told CNN.

Coalition air power was not evident in the region, but earlier in the day, the United States did turn its air power on more ISIS targets, taking out vehicles in other parts of Syria and Iraq and destroying a command node and a checkpoint.

Why it will take so long

The strikes are having some effect, experts say.

"We've been able to blunt the momentum of ISIS in Iraq," said CNN military analyst James Reese, a retired U.S. Army special operations officer.

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Airstrikes also have disrupted ISIS safe havens on the ground, such as the northern town of Raqqa, Reese said.

Kurdish Peshmerga fighters helped drive the extremists back and secure positions on the ground. Strikes have since targeted ISIS throughout the swaths it holds, and the combined efforts have stopped ISIS from swarming over Baghdad.

But the group's command structure is adapting to the attacks, said CNN military analyst Peter Mansoor, a retired U.S. Army colonel. It is spreading out, and its leaders are now "mixed in with the civilian population," he said.

"So, it's unlikely these airstrikes have crippled ISIS," he said.

And that's why the battle will take so long, Cameron said. Western infantries will not gun down ISIS fighters. That will be the task of local forces.

But in Syria, the marshaling of an effective ground partner against ISIS terrorists -- who have a victorious track record there -- has only begun. In Iraq, the military has been plagued by debacles.

Over the weekend, ISIS overran the Iraqi Sejar military base just east of Falluja, killing at least 113 troops, according to Iraqi officials. The fate of 78 others is unknown.

ISIS claimed to have killed nearly 300 Iraqi troops in the onslaught. It also reported destroying 65 Iraqi military vehicles, including 41 Humvees, and seizing 37 others.

Surviving Iraqi soldiers said their pleas for backup went unanswered by military commanders for hours. They were left stranded, they said in an online video.

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Iraqi officials said they had tried to support them but failed.

"There is no leadership in the Iraqi army right now," said retired U.S. Air Force Lt. Col. Rick Francona. "The people who are paying the price are the soldiers in the trenches."

Iraqi soldiers have been known before to abandon their weapons and run, giving ISIS an opportunity to collect them, Reese said.

ISIS is aggressive and dedicated

ISIS has a decided advantage over Iraqi troops, said Bill Roggio, the editor of the Long War Journal, which provides information and analysis on global terrorism and efforts to combat it.

"It's a level of commitment the Iraqi forces don't display," he said. "You can't coach aggressiveness."

"ISIS has managed to defeat Iraqi troops, Syrian troops, other anti-government fighters in Syria, and they've done it all at the same time."

The group is also good at recruiting, motivating young men and women around the world to join them -- including hundreds from the United States and Europe. It has also called on "lone wolf" actors to carry out terror strikes in the West.

Spanish and Moroccan police arrested nine men accused of sending foreign fighters to join ISIS, the Spanish Interior Ministry said Friday. A Spanish citizen headed up the cell, and his brother, a former Spanish soldier, is currently fighting with ISIS, the ministry said.

Analysts Reese and Francona agree that to make Iraq's army more effective, U.S. special operations would have to replace its command structure, which is melting away.

"The problem with that is, that is the definition of boots on the ground," Francona said, something President Barack Obama has promised wouldn't happen.

cnn.