The Iliad, Homer tells us, is about the rage of Achilles and the will of Zeus, and about how these two interact with each other. Quoting Lattimore:
Sing goddess the anger of Peleus son Achilleus
And its devastation, which put pains thousandfold upon the Achaians,
Hurled in their multitudes to the house of Hades strong souls
of heroes, but gave their bodies to be the delicate feasting
of dogs, of all birds, and the will of Zeus was accomplished...