The NATO angle (Why NATO would care about Syria)
The North Atlantic Treaty Organization (NATO) may well be the ostensible leader of an attack on Syria.
One might ask what the heck Syria has to do with maintaining the defensive security of America and Italy and the UK and such. But the NATO case in Syria is actually a little more sensible than the case was in Libya.
This is not an argument in favor of striking Syria. Only an explanation of how or why NATO would be involved. (Whether one calls this reason a motive or a pretext is up to the individual.)
Due to peculiarities of geography and the limited speed and range of early nuclear missiles, Turkey used to be key to restraining the Soviet Union. (We ended the Cuban missile crisis by secretly agreeing to remove our nukes from Turkey, which is, as the crow flies, pretty close to the old USSR.)
So we included Turkey in NATO.
And NATO member Turkey shares a long border with Syria. And millions of people fleeing war in Syria are crossing into Turkey, and that is burdensome on Turkey.
So Turkey says, "Hey, my NATO brothers... this neighboring country is threatening my security." Which it is, to some arguable degree.
So that's why the NATO connection here is stronger than the NATO connection when NATO acted against Libya.
That is not to suggest that NATO's real primary motive would be Turkish security. I don't know that to be the case or not to be the case.