In Catch-22, Joseph Heller's lead character Yossarian begs to stop flying because "they're trying to kill me." His comrade contends, "They're trying to kill everyone." Yossarian asks, "What difference does that make?"
He's technically not wrong, and, while quite different in tone to Heller's satire, Nolan's film similarly extracts and examines the essence of "what is happening now" and disregards any wider geopolitical context. Enemies are out to get our principal character (Fionn Whitehead's Tommy), and while we know it's the German Luftwaffe, they could just as easily be vampires or harpies.
The first killings come with nightmare logic. While scrounging for sustenance in an abandoned seaside village, unseen snipers gun down everyone to Tommy's left and right. All Tommy wants to do is take care of base needs: a drink of water and someplace private to move his bowels. He's unable to find relief (have you ever wanted to do something similar in a dream?) and is interrupted by the intrusion of pure terror. He ends up on a beach, where he silently watches as random death rains down on him from above.
He hits the sand as bombs fall. There's no point in moving -- he can only hope the shells stop before they reach him. The blasts summon bodies from Earth straight up in the air like you might expect from a science-fiction tractor beam, making Dunkirk less reminiscent of the gory first chapter in Steven Spielberg's Saving Private Ryan than the director's panic-inducing attack in War of the Worlds.