Death

War is death. That's pretty much a cold hard fact. And in a poem about war, we expect there to be plenty of death. And there's plenty o' death in this baby. The maiden's lover, the babe's father, the mother's son—they're all dead by the end of this short poem. And of course that's to be expected when they fight on a field that is littered with a thousand corpses.

• Line 2: The maiden's lover "threw wild hands toward the sky." This most likely means that he got shot or stabbed and threw his hands up as he was dying, which gives us an image of death, rather than just telling us straight up that this guy is no longer with us. 
• Line 3: The lover's horse rides off alone, which symbolizes the fact that the lover is dead. It might also point to the fact that this woman is now alone, without her counterpart, who died on the battlefield.
• Line 8: The speaker appears to be looking at a group of soldiers and says they pretty much were born to be drilled and die. This makes them seem like cattle, cogs in a machine, you name it.
• Line 11: Here again is an example of the speaker's cruel irony. We're prepared for a description of some kind of awesome kingdom and instead it's a… field with a thousand corpses. Yikes.
• Line 13: The babe's father tumbles into a yellow trench. He must have been wounded, which explains why he "tumbles" rather than jumps or dives. 
• Line 14: The father "raged at his breast," took his last swallow, and died. It's quite the graphic description.
• Line 18: The colors of the eagle's crest (red and gold) symbolize death and war. Red obviously reminds us of blood, and gold reminds us of that gross yellow trench from line 13.
• Line 20: The speaker talks about pointing out to his soldiers the virtue of slaughter. But, um, slaughter is totally not virtuous (well, maybe it is to the jerk speaking), so this is definitely irony. Unfortunately, it seems like no one in the poem, and perhaps least of all the speaker, really gets this irony. Only we, the audience, do, making this dramatic irony. 
• Line 21: The speaker continues, telling somebody to make plain to his soldiers the excellence of killing. There's nothing excellent about killing, so you might think of this as yet another example of dramatic irony.
• Line 24: The mother's son is wearing a shroud, which means he's dead. The tone of "bright splendid" is one of mockery. Once again: irony. There really is nothing bright or splendid about the sheet covering a dead kid.