Lets say there are 2 factions at war. One Evil and One Good.
Evil people can just ignore international laws and commit war crimes, Good people will have to abide by laws. Evil people can use torture to obtain information, while Good people aren't gonna use torture (because then they are no longer good by definition). Evil people can use chemical weapons and just attack indiscriminately, Good people have to make sure they don't accidentally attack civilians.
Good people are going to be against Nuclear Weapons, but Evil people doesn't care.
It seems like Evil is just more powerful. Do you believe that Evil is more powerful than Good? Why or why not?
I mean, we could have the "Good" faction starting to use Evil tactics, but then they aren't "Good" anymore, so the best we can get is a shadow of Grey, because truly Good people would just lose every time.
See Example:
Country A: Good
Country B: Half Good Half Evil
Country C: Evil
Country A would oppose nuclear weapons, while Country B builds them reluctantly (remember, they are only half Good), Country C builds them without any hesitation whatsoever. The result is Country A is doomed to fail, and an arms race between Country B and Country C. Good people always lose.
Your question is loaded with too many assumptions. You assume international laws as they stand are good as they stand, you assume torture works to obtain information, but more than that you assume these forces exist in a vacuum. By your logic and with your assumptions obviously evil is more powerful but you've papered over so much that the answer to your question is meaningless.
There is also the materialist part of your problem which is it assumes both sides have access to the same resources (and that they work the way you think they do). How many more Good people are there than Evil? Do the Evil people have the knowledge and skills to produce the weapons to facilitate the tactics you lay out or would they rely on Good people to produce them? If they do then what happens if the Good people object to making the weapons that facilitate their winning tactics? How can the Evil people conscript the Good people into performing their duty without those weapons?
Finally it assumes states act in unified ways under central control, and that everyone in those states are state actors and act under command of the state. There is no country in the history of the world where that has ever been true, not only does it go against the concept of free will (which your name suggests you don't believe in) it also assumes that either states are conscious entities of themselves or there are conscious people controlling these states and every single person in them or acting on their behalf.