If you're interested in the topic of war, you may like to check out the Just War Theory. Part of it forms the backbone of the Geneva Conventions, which is the internationally drawn up agreement for military engagement between countries.
There are three concepts in all:
Jus ad bellum
Jus in bello
jus post bellum
The first sets out the acceptable conditions for going to war. Seven concepts in all.
The second sets out the conditions for right engagement in a war. Three principles governing.
The third--a newer addition to the theory--concerns the administration of justice after the war. 5 concepts in all.
wiki has quite a good beginning article on the Just War Theory, as well as the comparative arguments for and against Just War.
Just War - Wikipedia, the free encyclopedia
For me: no, it makes no sense to follow rules in war. The fact that you're going to war, means you want to win. If so, whatever and any methods necessary for success have to be taken. After all, it is the winners who write the history books.
random aside: Those who were for the Iraq war may like to note that under the international codes of war, it was not a just cause. Nor was it ever sanctioned by the rest of the world.