I think those problems are a little different. For example, no matter how you approach it, from a rational point of view joining a war for your country makes no sense. You are highly likely to die and highly unlikely to change to outcome of the war.
But if you think in an evolutionary sense, if each individual in a tribe acted rationally, we'd get a sort of Tragedy of the Commons: the enemy tribe wins the war, and slaughters your men. So it may happen that if each individual acts rationally the group, each individual included, suffers; so it makes sense individual sense to develop mechanisms to go to war, which by symmetry must include yourself.
Even less intuitively even if the probability of death is lower by not going to war (no tragedy of the commons in traditional sense), which means no individual would rationally choose war or develop mechanisms to force going to war, it would be rational for the tribe to choose war, in an evolutionary sense, provided many more of your men are killed than the enemy tribe (so they do better in evolutionary terms).
I know I've heard this before, and I've not taken an evolutionary biology class before so I do give a lot of weight to the idea that there is little influence at the group level, but one of the first paragraphs states: "As of yet, there is no clear consensus among biologists regarding the importance of group selection."
In particular, when selecting for war, there's a clear individual level selection pressure: if you don't cooperate with your group, you likely die. This is a just so story, I have no idea how irrationality actually developed, but say you have small groups of hunter gatherers and one individual develops a preference for cooperating in raids against their best interest. If this means that on average you now have two versus one whenever this individual participates, there's a clear competitive advantage which could allow that gene to propagate. The key here in this hypothetical is that the mutation occurs at the individual level in a lone individual, who then cooperates with someone else who wouldn't necessarily follow them, but is happy to have the help. This results in a disproportionate gain (100%) in effectiveness vs lone opponents. As time evolves, the gene becomes more widespread by its early disproportionate effectiveness and groups that fail to cooperate are killed on average, thus eliminating individual competitor genes.
Again, I have no idea how war actually evolved, but it seems easy to believe that when a trait influences whether one group kills another, that it would cause the killers to have a reproductive advantage. I'd love someone more educated on this topic to send me up though.
But if you think in an evolutionary sense, if each individual in a tribe acted rationally, we'd get a sort of Tragedy of the Commons: the enemy tribe wins the war, and slaughters your men. So it may happen that if each individual acts rationally the group, each individual included, suffers; so it makes sense individual sense to develop mechanisms to go to war, which by symmetry must include yourself.
Even less intuitively even if the probability of death is lower by not going to war (no tragedy of the commons in traditional sense), which means no individual would rationally choose war or develop mechanisms to force going to war, it would be rational for the tribe to choose war, in an evolutionary sense, provided many more of your men are killed than the enemy tribe (so they do better in evolutionary terms).