Saying that the invasion of Iraq isn't responsible for increasing this kind of thing, because there were terrible things happening before that took place is a bit like suggesting that Bloody Sunday didn't help the IRA recruit, and encourage and enable it to extend its activities, on the grounds that there had been IRA Bombings before Bloody Sunday.

There is a kind of logic in saying "pulling outr of Iraq woudl reward the bombers and encoyrage them" - but it's got to be set against the clear evidence that the continuing presence of occupying troops actually generates militancy and terrorist activities, both in Iraq and outside it.

Basically, if you are stuck in a hole, the first thing to do it stop digging it deeper.