To my memory, the US funded rebel forces against Assad in Syria. This unfortunately included ISIS. It was not however created by the US directly, they formed after they US invasion of Iraq.
Same thing happened with the Mujahdeen when the Soviets invaded Afghanistan. The Mujhadeen then developed into Al Qaeda.
With the plane, this is turning into a mess. The Egyptian government are denying that it was a bomb (likely to keep their tourism industry safe) and Putin is saying the same (refusing allegations that it was his choice to bomb Syria). 29 flights were meant to safely bring back British tourists but only 8 planes brought people back. The Egyptian government grounded the others.
For once, I kinda respect David Cameron for releasing information that this may have been ISIS, rather than trying to cover it up.
Security was allegedly poor at the Airport where the plane took off too (people could pay to skip security checks), and "UK spies" have found supposed evidence that an employee at the airport smuggled a bomb onto the plane.
Either way, this is getting confusing and convoluted. ISIS have claimed it was them, but refuse to release the details of what they did (suggesting that they are bluffing to spread terror).
The worst part though? If it is ISIS, they now know they can get away with things like this. They may try again.
Evidence that the explosion happened inside the plane.http://www.telegraph.co.uk/news/worldnews/europe/russia/11978962/Russian-plane-crash-sharm-el-sheikh-stranded-British-tourists-latest-updates.html