Rama send Angadha as peace envoy before the war start. Krishna goes himself as peace envoy before the great war. There is always first try to resolve by peaceful process and eat is last resort.
Along these lines...did Rama try to convince Vali to give up his hatred towards Sugriva and and also Sugriva's wife?
It doesn't look like peace talks were on the table as both Rāma and Sugrīva had already made up their minds that Vāli should be eliminated.
http://valmikiramayan.net/utf8/kish/sarga5/kishkindharoman5.htm
"Oh, Raghava, my brother denounced me, he even made me an enemy of his, such as I am I am living in these forests with scare and fear, and with dismayed vitality... [4-5-22b, 23a]
"Oh, highly fortunate Rama, affirm fearlessness to me from Vali by who I am highly intimidated, and as to how there will be fearlessness to me from him, it will be apt of you to accomplish that, that way... [4-5-23b, 24a]
When thus said, that resplendent and righteous one being the patron of virtue Rama replied Sugreeva, as though laughing off. [4-5-24b, 25a]
"A friend is the resultant factor of helpfulness... that I know... oh, great monkey I intend to eliminate that Vali, the abductor of your wife... [4-5-2b, 26a5]
"Unfailing are these arrows of mine, scorchers like sun, sharp ones tied with eagle feathers, similar to Indra's Thunderbolts, sharp are their point and straight is their egress, similar to enraged snakes, and these arrows of mine will be speeded up to fall on that vicious Vali... [4-5-26b, 27, 28a]
"You will see now itself the falling of Vali like a splintered mountain onto ground, when completely ruined by these cruel arrows that are similar to venomous snakes..." Thus Rama inculcated confidence in Sugreeva. [4-5-28b, 29a]
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http://www.valmikiramayan.net/utf8/kish/sarga12/kishkindharoman12.htm
"Oh, Rama, today itself you eliminate that enemy of mine in a brother's semblance for my happiness, for which I adjoin my palms in supplication." Thus Sugreeva requested Rama. [4-12-11]
