It affects the US in a few ways: 1. It is destabilizing the region, threatening to engulf Jordan, Iraq, and Lebanon into full-scale conflict. 2. It is putting extra strain on the aforementioned states as a result of the influx of refugees each day. This further destabilizes the region, making more conflict all that more inevitable. 3. It is allowing al-Qaeda to grow stronger. 4. The influx of foreign fighters from the US and European countries scare the shit out of us, if I'm blunt. These guys are gaining valuable first hand knowledge of how to conduct guerrilla warfare and/or terrorist tactics by al-Qaeda; we worry that when these guys and women return, they will utilize their new found skills to conduct terrorist attacks in their country of origin.