I heard of a story in a lecture about women negotiating a peace treaty when their kings (spouses) wouldn't stop the war. They did it to keep from losing more sons and family members and met somewhere without the men. I am trying to confirm this for a paper and can't find it anywhere. Was there a treaty brokered by the women? I was sure it was pre WWI and probably medieval and somewhere in Europe...
I am just about certain that no such treaty exists in real life. I am inclined to think that you are remembering someone who told the general story from the play Lysistrata by the ancient Greek playwright Aristophanes. That play was written Athens in 411 BCE. Its plot is not exactly like the scenario you describe, but it is rather similar.
In the Lysistrata, Athens and Sparta are at war. The women of Greece want the war to end for the same sorts of reasons that you mention in your question. Women from many of the city-states of Greece get together and the leaders persuade them to go on a sex strike. They will refrain from having sex with their husbands until there is peace. The idea is to force the men to make peace even though they do not really want to.
In this play, the women do not actually negotiate the treaty among themselves. Instead, they force the men to agree to meet and they help to guide the negotiations to ensure that the men really do make peace. The men eventually do make peace and it is all due to the influence of the women.
While this is not the exact situation you describe in your question, it is the only thing I can think of that resembles that scenario. I do not believe there has ever been a real-life example of this happening between countries.