General Discussion

Sneak attacks are part of warfare. There's no rule stating that wars have to be declared before hostilities commence. Nowhere is it written that they have to send a telegram or a bloody glove or something.

Declaring war before the attack would have undermined the entire point of the attack from Japan's point of view. They wanted to cripple the Pacific fleet and lock America out of being able to project force in the western Pacific Ocean. Catching the fleet at anchor allowed them to target them all in one place. If they'd declared war in advance that opportunity would have been lost.

You can make an argument that the attack on Pearl Harbor was cowardly but the point of war is to win, not look super cool and brave.

This warship was on its way to an active combat zone. Taking out enemy reinforcements before they get into position to be effective is also part of war. The fact that it was in international waters means absolutely nothing.

As it turns out, war is hell. I seem to recall some military type saying that once upon a time.