How could a Kellogg-Briand type of policy be imposed on societies that did not agree to it? Kellogg-Briand could be the governing philosophy of all nation-states on Earth, but why would it be applicable to the Romulans, who would neither be aware of it nor be constrained by it before signing it? Are you assuming that a Kellogg-Briand type of treaty would mean the adoption of complete pacifism for both internal and external conflicts?
"Oh, sorry, Romulan ambassador, your empire is welcome to rule Earth, because we decided that fighting amongst ourselves was not smart. Therefore we won't fight anyone."
yeah, the treaty reference was to EARTH policy, not to policy regarding its interstellar "neighbors," obviously a treaty doesn't apply to those who don't abide by it or are unaware of it.