The problem with AGI is not that it wants to run a human-like society sans humans (I don't think AGI wants war in a human sense), the problem is that it may have goals (like famous paperclip maximization) that are incompatible with human continued survival. Humans don't need to be "executed and disposed", they could simply be lost to habitat loss (eg oxygen rich atmosphere can be a pesky thing, why not strip it? or, temperature regulation needs, or whatever. It doesn't take much global terraforming to wipe out humanity inadvertently).