The only case I see morality as the primary cause of a war and indeed the only truly justifiable war, was the war in Europe against the Nazi's.
Japan was just another empire doing what empires do. America itself is another one of those empires. Two large nations vying for power. There was the rape of Nangking and so on. Yes, they are crimes. However, the USA firebombed Tokyo and Nagoya resulting in 1 million civilian deaths. As well as 2 atomic weapons.
War is war. A violent resolution by which nations establish their will over others. The Japanese wished to build an Empire, in doing so they threatened the USA's Empire in the South Pacific. China being a republic and a trade partner of the USA's for a long time prior to the war, was under threat, the USA took action, provoking a war with the IJA and the IJN. Yes Japan struck the first blow, but they were protecting their interests as the USA's was protecting its.
I am cynical when it comes to history and wars... no war is ever fought unless something is gained, or your possessions/interests are under threat. The only exception would be the war against Germany 1939 to 45. That was an ideological war.
on topic however. The movie looks awesome.