The images of war in the poem are pretty stark. In lines 25-26, the speaker refers to the reason that the people of Vietnam no longer live in peace. In this alternate future, bombs were dropped, destroying the entire country. Line 16 sees the mouths of the people burnt by these bombs, and line 18 shows their bones "charred." While in actuality bombs didn't destroy all of Vietnam, war certainly caused its share of destruction to the people there. Many images of the conflict became popular tools for anti-war protests; it kept those far from the conflict informed and, well, appalled. Maybe that's why Levertov doesn't hold back when it comes to the imagery of bombs and destruction in this poem.