The failure of the Rule of Man triggered the collapse of most interstellar civilization. While interstellar travel and commerce continued, it was at a greatly reduced rate, and the many worlds of the Second Imperium turned in on themselves. The period of collapse is termed Twilight, and it lasted for two and a half centuries.
Modern historians consider Twilight to have begun in -1776 when the treasury on Hub/Ershur (Massila 0402)refused to acknowledge a monetary issue of the branch treasury at Antares, which triggered a financial collapse and the destruction of large-scale trade within the Imperium.
The end of Twilight is commonly accepted as the year -1526, when the last government claiming to be the Rule of Man ceased to exist. This led into the deepest part of the Long Night.