Resources. There is a pipeline that runs from iraq, through iran, syria, under the ocean, all the way to greece.
Russia claims the pipeline is a Nato conspiracy to take away from their exporting of oil and gas.
America doesn't want to lose the pipeline and give the crazy muslims any more money to buy stupid shit.
Europe doesn't want to lose a shit ton of profit and resources.
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Also saudi arabia has been funding ISIS and other terror groups for decades now. That's something to always take note of, Saudi Arabia is like the donald trump of the middle east (but actually rich and powerful), so they just pay people off to benefit them selfs in anyway.