Event Description
The destruction of the Trisolaran homeworld by a photoid served as a stark warning to humanity — the solar system's coordinates had been exposed, and a similar strike could arrive at any moment. Based on analysis of known "dark forest strike" methods, humanity deduced that attackers would most likely use a photoid to destroy the sun. Operating on this assumption, humanity devised the Bunker Project: constructing large-scale space city clusters behind the four gas giants at the solar system's outer reaches, using the giant planets' enormous mass as natural barriers to protect city inhabitants when the sun was destroyed.
The Bunker Project was an engineering feat without precedent. Hundreds of space cities were built in orbital positions behind Jupiter, Saturn, Uranus, and Neptune, each capable of housing tens of millions of people. Billions of humans migrated from Earth and other inner planets to these space cities. Humanity established complete social systems within these cities and continued civilizational development. However, the Bunker Project contained a fatal assumption flaw — it presumed the attack would come in the form of a photoid strike on the star. When the actual attack arrived, it employed an entirely different weapon — the two-dimensional foil. The dimensional strike did not target the star but reduced the spatial dimensions of the entire stellar system, rendering the Bunker Project completely ineffective against a dimensional attack.