It's hard to miss the overall anti-war tone of the poem. After all, it depicts an entire people destroyed—along with any legacy they could have left behind—by the violence of war. That perspective is no accident. Levertov was an outspoken critic of violence and worked for much of her life as an anti-war activist. The poem advocates for the preservation and respect of human life, and this—plus a clear stance against violence—is present in many of her poems.
Just check out "Life at War" for another example of Levertov's outspoken, poetic opposition of war.