"He who does not think himself worth saving from poverty and ignorance by his own efforts, will hardly be thought worth the efforts of anybody else." -- Frederick Douglass, Self-Made Men (1872)
This "gang" is called The Turkish Youth Union, and it is opposed to the current Turkish government, a government which has lately turned on its own people with the violent clashes last year. This was not an opportunistic group of street thugs; this attack was scripted and organized. The Turkish government is Islamic, and a large contingent of Turkish people are secular, so we've been seeing these clashes become more and more unstable.
The current Turkish government has been more and more vocal in its displeasure with the US, so to see an avowed enemy of that government seek out US military members for a scripted and organized attack is frankly concerning to me. If the Islamic government is hostile to the US and the secular opponents of that government are also hostile to us, this does not bode well for our military in particular and NATO in general.