This is cartoon parable. Despite the fact that mankind is killed, the war still continues. War continued with automated system left by people. One of the last surviving bomber and its pilot still performs its task. The city is dead for a long time. Dead people who built it. Dead people who gave the order to destroy the city. And war will continue until subside echo of humanity. But life will always find a way to survive. Cassette bomb sub munitions became a fortress for the grass.