We never learn. I've filched from Wiki:
"In 1843 British army chaplain G.R. Gleig wrote a memoir of the disastrous (First) Anglo-Afghan War, of which he was one of the very few survivors. He wrote that it was....." :
"......a war begun for no wise purpose, carried on with a strange mixture of rashness and timidity, brought to a close after suffering and disaster, without much glory attached either to the government which directed, or the great body of troops which waged it. Not one benefit, political or military, was acquired with this war. Our eventual evacuation of the country resembled the retreat of an army defeated.[11]" (Sound familiar ?)
And now we hear, in all the Media, the universal lament about What Must be Done, and Should be Done, and What Needs to be Done, and the assembled Might of the UN and Security Council has been invoked, and evildoers tremble (?). And our Home Secretary announces that Further Legislation will be introduced..... (Small Mouse pipes up: "But who'll Bell the Cat ?" )
The brutal fact is that President Assad will have to be brought on board before anything can happen, for we cannot, and President Obama will not, put "boots on the ground", and ISIS will not be defeated in any other way. That we do not like him, and that he was yesterday's "baddie", is irrelevant. Seventy years ago we did not like Stalin very much, but we were glad to have Russia as our "Gallant Ally".
And:
"If Hitler invaded hell I would make at least a favourable reference to the devil in the House of Commons." - (Winston Churchill).
Your enemy's enemy is your friend !