My general rule of thumb is that there are no things important enough to go to war over, other than stopping a war someone else has started.
I cannot readily think of a scenario in which a war yields a better result than alternatives like diplomacy and trade.
But of course, some day somewhere, somehow, some regime will be committing such atrocities that a war could be a better alternative, rendering my rule of thumb useless. Before entering though, you had better make sure that you can win this war without creating more misery than you come to end.
War,after all, creates so much misery that I would rather err on the side of caution.