- The Long Night was a period of intense anarchy, widespread tragedy, and interstellar disaster between the fall of one major polity, the Second Imperium or Rule of Man, and the succeeding polity, the Third Imperium.
- Also called an interregnum and represents the historical period extending from the Second Imperium to the Third Imperium.
- A timeline in Traveller: The New Era gives 2992AD or -1526 as the start date of the Long Night [p.9].
- The galaxy is only just emerging from this period which is commonly held to be from -1776 to 0 according to the Imperial calendar.
It was a period where worlds were cut off from one another, technology was lost and the population on many worlds simply failed to survive.
It could be said that the First Imperium was "meta-stable": stable, but only because of active effects enabled by its stability. Disrupt it (such as by the slow decay that was already occurring prior to the Interstellar Wars, or by said wars themselves), and it would not naturally return to its prior state.
The main facilitator of this meta-stability was trade. Many worlds depended on routine import of components - manufactured things, rare ores, or the like - not locally available. Once routine import was disrupted, the colony's capabilities deteriorated (in many cases, life itself became impossible, resulting in a Dieback World), so it could not in turn supply its unique components that other worlds depended on. There were a few worlds with all the basics to support their own technologically advanced civilization, but as the worlds around them collapsed, supporting them - previously a profitable activity - often became unprofitable, then unsustainable, and in those cases such efforts eventually ceased.
Many of the "false dawns" (which seemed to offer an end to the Long Night, but did not last) were centered around a brief resurgence in interstellar trade that turned out to be unsustainable. The birth of the Third Imperium was as much about financial engineering (learning from over a thousand years of failed attempts all across the former Imperiums) as about Fusion+ or any other specific factor.
It has been noted that even the Third Imperium can not expect to live forever, which some use to question whether the Third Imperium itself is a false dawn. While it is true that such measures are subjective, the fact that the Third Imperium was still around and actively expanding at the end of its first century set it leagues above most other dawns. When the end of its second century saw the same status, there were no officially recorded objections from the few sophonts in Imperial space who were alive (via anagathics, low berths, or other measures) in both 0 and 200.