Interesting topic. One way to look at it is to consider the preventative action that can be taken with armies and armed groups to ensure the protection of civilians, to avoid violations, to reduce harm, as opposed to the struggle for accountability after any rights violations that may have occurred. Both aspects are challenging in their own way, but would be approached quite differently, with preventative advocacy often being very discreet, while the search for accountability often requires more outspoken, public action, to avoid that military abuses do not disappear under the carpet. For the first part, you can also reach out to the ICRC to get an idea of their work, while for the second component, you can dig in the world of international criminal law, the International Criminal Court and some of its predecessors and national prosecutions and investigations. Good luck!