World War III

What happened? There's only one stone, no date.
Only a few fortunate ones were buried at all. It happened so fast, families were buried together. Dates became unimportant as all systems broke down. Finally, there were no more armies or fighting. Only starvation, contamination and lingering death.

 — William "Buck" Rogers and Dr. Theopolis after Rogers comes across a surviving gravestone for his parents, Buck Rogers in the 25th Century's "Awakening"

World War III is a pivotal point in Earth's history.

Occurring later in 1987 CE, William "Buck" Rogers escapes a calamity that befell his planet and time aboard Ranger 3, despite his attempt to remedy it (BR25: "Awakening", "Testimony of a Traitor"). Sometime during 1987, Hieronymus Fox creates his own cryo chamber protoype, using it to preserve himself (BR25: "Cosmic Whiz Kid").

Returning home in the year 2491 CE, Rogers discovers that his parents are buried in Old Chicago, their graves marked with a singular family stone. Dr. Theopolis informs Rogers that the war caused a great calamity to befall the entirety of Earth, with the survivors having to deal with starvation, contamination and lingering death (BR25: "Awakening").