Explanation:

- Option 1: ex post facto justice relates to the legal application of laws to actions that predate the laws themselves. While controversial aspects of Nuremberg and Tokyo trials, it's not their main legacy.

- Option 2: international law is correct. The Nuremberg and Tokyo Trials were pivotal in establishing principles of international law and accountability for war crimes, influencing future international legal standards.

- Option 3: the Geneva Conventions predated these trials; although the trials reinforced the need for international humanitarian law, they did not directly develop these conventions.

- Option 4: standards for human rights were influenced by the trials, but the primary outcome was the development of international law frameworks.