Both texts explore the concept of power and fulfilling one's ambitions at the expense of others. In both cases, those in power became transfixed by their own ambition and it was the innocent who suffered. In the case of Macbeth, the uncontrollable ambition Macbeth experienced was also his downfall as he became complacent. Therefore, the innocent around him suffered (his wife, who died without him even caring, Banquo, Fleance, Malcolm, Macduff and his family) and eventually Macbeth himself. Dulce et Decorum is directed at military generals. The persona is sarcastic in tone when he quotes the generals, "dulce et decorum est pro patria et mori". It was the drive of power and ambition that led those with military power (generals, commanders, governments) to push on against stalemate, when they were outnumbered, when hundreds of their men were being senselessly killed. In the end, just as in the case of Macbeth, this becomes their downfall. They have lost respect. So, in a sense, both texts act as cautionary tales, warning their responders away from unbridled ambition because it has such a tough downfall.
The two texts also share the theme of guilt and use the image of the dream to explore this. Both Macbeth and his wife experience dreams and/or hallucinations that emphasise how guilty they are really feeling. Similarly, the persona in the poem feels guilty about not being able to save the man killed in the gas attack and somewhat embarassed about the way that the man was treated. The man's face haunts the persona just as Banquo haunts Macbeth and Lady Macbeth is tormented by blood stains.