Obama seems to say what happened in Syria (regardless of the culpret) is in the USAs " national interests". Why so? I do understand the humanitarian issue, but- specifically what makes it Syria all of a sudden of USAs "national interest"?

BTW, I understand Russia and Iran s interest in the area- but, I am inpuzzled by China s interest in this issue (I expect it may have in intrerest in bankrupting the USA through foreign conflict, as it is a major banker).