The Enterprise visits planet Omicron-4
(sound of transporters, as Captain Kirk, Mr. Spock and Dr. McCoy materialize on the planet's surface)...
Kirk: Mr. Spock, begin sensor readings immediately.
Spock (flips on tricorder): Captain, there is evidence that this planet, known as Omicron-4, once was inhabited by a large numbers of human creatures with a moderately-advanced civilization, at least for their time. But they seem to have almost entirely disappeared as a result of a sudden catastrophe.
Kirk: What kind of catastrophe, Mr. Spock? Advanced populations don't vanish without leaving something behind...
McCoy: Jim... picking up evidence of human-like creatures in those caves in the hills in the distance.
Kirk: Very well, doctor, we'll investigate.
(on the way to the caves)...
Kirk: Mr. Spock, what do you make of these large towers with the cabling between them?
Spock: Captain, sensors indicate that they may have been used for the purpose of electrical transmission. Although the method seems primitive by our standards, they were efficient enough in their own time. However, they seem to have been unused for years...
Kirk: Mr. Spock, your analysis, please.
Spock: Apparently, Captain, there was indeed once a thriving civilization on this planet. They had many natural resources providing multiple sources of carbon-based fuels with which to power their economies and technology.
But there appears to have arisen a faction of elites in control, who somehow acquired the delusions that their human activities were changing the climate of Omicron-4, and that the only way to prevent such change was to abandon natural carbon-based resources and implement unsound alternative methods of powering their economies, methods that were unreliable and inadequate.
As a result, sir, when the fossil fuels were driven from production, the Omincrons' economies, technologies -- and ultimately, their civilization -- collapsed with amazing speed. And by then, having lost their acumen required to restore functions based on their previous fossil fuels, recovery became impossible.
Hence, the backward inhabitants we see today.
Kirk (opening communicator): Scotty, beam us up. There's nothing we can do here.
(Sound of transporter as the landing party energizes and disappears)