specification of war

Recently I heard a talk about definition of war. We also hear the phrase 'rules of war'. This post puts those two togather.

It seems there are two definitions for war: 'Industrialized war' and 'Non-industrialized war'. Popular opinion is that Industrialized war is lawful. US Govt. often makes this point while justifying drone and Iraq war. I want to go back to colonial times of occupation of India by UK. During those times UK was able to defeat Kings in Indian states using their superior fire power. UK used gun powder and Indian kings were using swords. Going by modern definition of war, UK and India were using 'Industrialized war' and 'Non-industrialized war' strategy respectively. And UK could have justified colonial occupation as legal war, though it sounds absurd in hind sight.

So the definition of war is not clear as black and white, especially given that US has not taken part in World court.