I know there's a lot of disagreement about this. Some historians say that women's performance of "men's work" in the war so impressed leaders that they felt women were to be trusted with the vote after all (this was true of Prime Minister Asquith, anyway.) Others think it had more to do with the fact that so many men had died, the government had no choice but to empower women. Or it's also been argued that as most suffragettes stopped campaigning during the war, it actually slowed them down. And my history teacher at school said women were given the vote after the war just to keep them quiet!
There are some very good articles about this topic here.
There are some very good articles about this topic here.