With respect for the prior question - in general terms any war that is historically recorded is important. We learn from history, no matter how biased or inexact it may be. Yet, it seems we never learn enough to understand that no war has ever resulted in the overview (justification for?) one side or the other subscribes too.
There cannot be "a most important war" decided; because we do not know the totality of any wars cause, impact or result. What was lost and/or gained, completely? Not just what is believed or selectively reported.
The sad thing is we might consider any war something to celebrate. This is done only when the misery and death accomplished is overlooked. Remember, the images we gain knowledge of during a conflict, the injury to mind, body and culture, too often shut away or edited from our societal mindfulness.
War is something to be rationalized, justified, while peace and respect-for-others is what is truly important. What is the most important peaceful outcome or continuance in human history?