Story highlights Qassim Shesho commands about 2,000 Yazidi fighters on Mount Sinjar in Iraq

He and his sons, all Iraq natives and German citizens, came after ISIS attacked Yazidis

"I decided to defend Sinjar, not to fight. They decided to fight," he says of ISIS

Shesho's son Yassir: "If it comes to it, then I'm ready to die here"

Qassim Shesho stands on Mount Sinjar in northern Iraq, overlooking a vast mountain range that rises from the desert. The calm is deceptive.

He worries about the village behind him. Sheref ad-Din holds one of the holiest shrines for the Yazidis. ISIS militants are only two miles away.

"ISIS wants to exterminate us and they want to establish an Islamic caliphate, but Islam is not like what they are doing to us," Shesho says. He says he commands about 2,000 Yazidi fighters.

Just months ago, he lived a peaceful life in Germany.

"I came back because my people are here. ISIS are terrorists. I came to defend my land, my family and my religion," he tells CNN by phone, speaking in Arabic.

He didn't come alone. Shesho's 26-year-old son, Yassir Qassim Khalaf, is with him. Yassir arrived in September, shortly after ISIS's initial attack on Yazidis left thousands stranded on the mountain without food, water or medical care. Their plight captured the world's attention.

Photos: Photos: Defending Yazidis' last stronghold Photos: Photos: Defending Yazidis' last stronghold Defending Yazidis' last stronghold – Qassim Shesho and his son Yassir Qassim Khalaf, along with four other sons, left a peaceful life in Germany to fight ISIS militants in Iraq. Hide Caption 1 of 6 Photos: Photos: Defending Yazidis' last stronghold Defending Yazidis' last stronghold – Shesho is the commander of the Yazidi Protection Unit in northern Iraq. He and his troops are defending the Yazidis who remain on Mount Sinjar near the holy shrine of Sheref ad-Din. Hide Caption 2 of 6 Photos: Photos: Defending Yazidis' last stronghold Defending Yazidis' last stronghold – Yassir arrived in September, shortly after ISIS' initial attack on Yazidis left thousands stranded on the mountain without food, water or medical care. Hide Caption 3 of 6 Photos: Photos: Defending Yazidis' last stronghold Defending Yazidis' last stronghold – Shesho, center, is in charge of about 2,000 Yazidi fighters in the mountain range. Hide Caption 4 of 6 Photos: Photos: Defending Yazidis' last stronghold Defending Yazidis' last stronghold – At one point, Shesho's five sons fought ISIS alongside him in the mountains. Three of them have returned to Germany. Yassir is still there, along with one of his older brothers. Hide Caption 5 of 6 Photos: Photos: Defending Yazidis' last stronghold Defending Yazidis' last stronghold – "I came back because my people are here. ISIS are terrorists. I came to defend my land, my family and my religion," Shesho told CNN by phone, speaking in Arabic. Hide Caption 6 of 6

The Iraqi air force and fighters with the Kurdish fighting force -- the peshmerga -- rescued some families in a dramatic helicopter mission. U.S. airstrikes helped clear a path for thousands of Yazidis to escape the mountain into neighboring Syria and to Iraqi Kurdish territory.

Yet the nightmare continues for thousands who remain on the mountain, surrounded by ISIS forces intent on eradicating anyone in their path.

"You can't just stay in Germany, live in luxury and leave your family and your people alone while you are watching it all on TV, thinking, 'It'll work itself out,'" Yassir says in German.

Shesho's troops, in many ways, are fighting an existential fight.

Yazidis are one of the oldest religious communities in the world, with a population estimated at only 700,000. They have suffered persecution through the ages. Many Muslims consider them devil worshipers.

Yazidis captured by ISIS have been forced to convert to Islam. Gruesome reports have emerged of Yazidi women being enslaved, raped and sold off by ISIS members while men and boys are executed.

The United Nations concluded that the actions of ISIS "may amount to an attempt to commit genocide."

He came to 'defend,' not to 'fight'

"I decided to defend Sinjar, not to fight. They decided to fight," Shesho says of ISIS. "We defend our land and our holy places. I have lived in Germany for 24 years and have always abhorred killing and fighting."

Shesho's troops receive weapons and humanitarian aid from the Kurdish regional government. Kurdish forces airdrop food and weapons. U.S. airstrikes on ISIS also have helped, but Shesho says it's not enough.

"ISIS wants to ruin the whole world. We want more American airstrikes between Sinjar and Dahouk so we can go back to our lands and live in peace."

At one point, Shesho's five sons fought ISIS alongside him in the mountains. Three have returned to Germany. Yassir and an older brother, Haydar Qassim Shesho, remain.

They keep in touch with friends and family in Germany as much as fighting and bad cellular reception allow. Yassir says his mother worries. They try to console her.

"Three times a week, we try to send her pictures and messages to say that everything is OK here and that she doesn't need to worry," Yassir says.

His mother and brothers are in a German town of 50,000 called Bad Oeynhausen, in the western state of North Rhine-Westphalia.

'I just couldn't bear to witness the suffering'

The family fled Iraq in 1990, when Saddam Hussein ruled the country. They went to Germany and eventually became citizens.

Yassir was 2.

"When I'm in Germany, I'm grateful that I'm able to be there. But if it comes to it, then I'm ready to die here," he says.

Before coming to Iraq, Yassir worked part time in crafts services for companies and hotels around his hometown.

"I actually wanted to be here from the beginning because I just couldn't bear to witness the suffering of the Yazidis. ... How our honor is tainted, how our families and wives are being captured," Yassir says.

"To go from luxury to war is not pleasant, but you gotta do what you gotta do."