A danish engineer's syrian friend was kidnapped. So he joined the YPG to fight Daesh.
http://www.dailymail.co.uk/news/article-3305121/Gently-hands-trembling-handed-grenade-threw-trench-exploded-instantly-flung-one-half-metre-air-dead-Ex-marine-reveals-moment-killed-ISIS-fighter-Syria.html
http://www.spiegel.de/politik/ausland/islamischer-staat-dieser-daene-kaempfte-gegen-den-is-in-syrien-a-1065430.html#
(article in german)
2003 Jorgen Nicolai (not his real name) worked as an engineer in Aleppo and made friends with a Syrian. They stayed in contact. 2014 his friend was kidnapped and never seen again. Jorgen Nicolai suspected, he was killed by Daesh.
Jorgen Nicolai tried to join the iraqi Peshmerga-Kurds, offering his services as an engineer. They declined.
He tried with the YPG. They agreed.
Meanwhile, his wife was pissed.
Jorgen wanted to do something against Daesh, but he was too afraid to actually fight. When he encountered other foreign-fighters at the YPG, he figured that he could join the fight and still have a chance to survive.
He was grouped with a squad of 4 North-Americans and Britains, most with military background. Jorgen had only basic military training from the time he had been drafted.
Jorgen was lucky. He was on fronts where the YPG was winning against Daesh.
He realized that he didn't fight for justice for his friend's death. It was bloody revenge. Pure and simple.
He's not proud of what he has done. And he doesn't want to talk about the killing. He knows how many people he has killed, because his squad kept track of that. But he doesn't want to talk about it.
He particularly remembers one firefight where he killed two Daesh-fighters with grenades and posed with a dead body for a photo afterwards. In hindsight, it seems surreal to him.
Jorgen left the fighting after 5 months and returned to Denmark. His body was bruised and he figured he would eventually overstay his luck and get killed. And there was this tiny problem with unpaid bills and a pissed wife waiting back home. And the YPG didn't pay him.
Jorgen would like to return to Syria. He misses the thrill of the war. And the sense. Just you and the enemy. Everything is so simple.
But he won't return. Because of monetary reasons and because of his wife.
Meanwhile he has moved to a different country. He's afraid, danish Islamists might recognize him.
And he has written a book about his time there.
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I don't know what to think about this. His whole story seems too perfect, as if it's a pitch for a movie. (Add a mentor-figure and you have "Hero's Journey".)
Plus, he returned to Denmark in May 2015 and his book "Heval" (310 pages) came out on August 31st. That seems MIGHTY quick to me.