Second Strike
Explanation
The Joke
The first panel shows a person from behind, looking at a scene of apocalyptic devastation -- massive pillars of fire or nuclear explosions rising from a burning landscape. This appears to be the aftermath of a catastrophic nuclear first strike that has destroyed civilization.
In the second panel, the same person turns around to face the viewer with arms spread wide and a gleeful expression, shouting: "Y'ALLLLLLLL!" The caption reads: "The Second Person Plural Wars arrive at their inevitable and brutal conclusion."
The joke is that the "Second Strike" referenced in the title is not a nuclear retaliation, but rather the final battle in a war over which second person plural pronoun is correct. The apocalyptic destruction was apparently caused by a conflict over regional variations of English -- and "y'all" has won.
The Humor
The comic works through a magnificent bait-and-switch. The title "Second Strike" and the imagery of nuclear devastation lead the reader to expect a serious commentary about nuclear war and mutually assured destruction. Instead, the "war" is about grammar -- specifically, the contentious question of what English word should serve as the second person plural pronoun. The person celebrating amid the ruins is a "y'all" partisan who has achieved total victory through nuclear annihilation of the opposition. The absurdity of treating a minor linguistic preference as worthy of thermonuclear war is the core of the joke. The gleeful "Y'ALLLLLLLL!" shouted over smoldering ruins is a perfect punchline image.
References
English lacks a standard second person plural pronoun, leading to regional variants: "y'all" (Southern US), "you guys" (much of the US), "youse" or "yous" (parts of the Northeast and also in some dialects of British/Australian English), "you'uns" or "yinz" (Pittsburgh area), and "ye" (Ireland and parts of England). This is a genuine source of (usually friendly) linguistic debate. The term "second strike" in nuclear strategy refers to a retaliatory nuclear attack launched after absorbing a first strike, a key concept in the doctrine of mutually assured destruction (MAD). The comic title puns on "second" referring both to the nuclear strategy concept and the grammatical second person.