War is one of the big subjects of epic poetry. It's what a lot of the famous Greek poets, like the ones our speaker looks back to, wrote about. But it's not her subject, at least not for now. What she does, though, is turn it into a metaphor for the scuffle she's about to start with the male critics who want to shut her up.
Line 1: Here she's referring to actual wars from history, the kinds where men beat each other to a pulp over land. That's not really the kind of poetic theme our speaker is interested in here—she's willing to leave that stuff to the guys.
Line 39: Here she changes the meaning of "war" a little, and suggests that she's in a kind of metaphorical war with the critics. She brings it up here only as a way of saying that she doesn't want to fight such a "vain" and "unjust" war. Still, it's hard not to feel like she could probably fight a war of words if she felt like it (and maybe she already has).