Although the Fall is linked to a number of events and cataclysms its single biggest trigger was the failure of the Second Republic welfare computers. At the time the republic had gained many enemies within and without. There was deep unease over high technology, corruption, high tax, unemployment and seceding planets. A wave of new think machines and robotics had lead to increased unemployment so the number of people affected was vast.
The Republic thought the Church was to blame as it had the means and the motive but terrorists and the Nobility were also considered. The failure triggered riots across republican space.
Amid the panic the fading suns phenomena first appeared pushing public panic higher. The Church charged technologists and the democrats with moral failings causing the dimming phenomena.
In a last minute effort to defend itself the Republic agreed to take on the church as the official religion. This only caused sectarian fighting to emerge. Perhaps threatened by a growing church and enticed by a weak Republic the Rogue Worlds military seized Byzantium in a lightning coup. In response to the hijacking of the government ten Noble houses gathered there military forces and retook Byzantium in an effortless fight that many saw as capitulation.
After the capital taken by the ten Houses the Republic was dissolved. The remaining officials were tried in summary courts, others fled to Criticorum while and some simply vanished. Infrastructure collapsed leading to plague and famine. Over the next few years the population plummeted.
To escape the chaos a large number of planets closed their Jumpgates and became Lost Worlds. In an atmosphere of revenge and distrust the the previous era the Church moved to prohibit the use of technology declaring them forbidden.