Space is absolutely huge. Scarcity of resources is a trivial problem compared to travel. That is, the odds of a finding a commercially viable alternative source

Space is absolutely huge. Scarcity of resources is a trivial problem compared to travel. That is, the odds of a finding a commercially viable alternative source of whatever element or small molecule or even habitable systems is wildly less expensive than war. Why bother fighting? The only consideration would be a situation where one civilization is so overwhelmingly more powerful, the annihilation of the weaker is trivial, like stepping on an anthill. Except the odds of your foot ever landing on an anthill approaches nil. Don't cross the street to get your ass kicked.