Human Recolonization

Within a few centuries, the Grand Canyon Ark had expanded to a new home of over a million citizens. In the protective walls of the canyon and isolated from the rest of the world, Bastion had grown into a huge, bustling metropolis; the largest city in the world and what may be the last safe haven on Earth for humanity. It contained towering skyscrapers and advanced infrastructure across hundreds of miles, all shielded within the mile high canyon walls. The city was designed to be self-sufficient, with its own power and water sources. Harsh weather conditions, difficult to acquire materials, and extreme radiation storms were all now manageable within the prospering capital. 
By 2300, expeditionary parties had been established to venture beyond the city and into the wastelands to explore what remained of the world and to attempt communications with any possible humans left alive after all this time. No contact had been made to the other Arks around the world, however a scouting expedition west towards Lake Mead discovered the presence of survivors. It ended poorly as they were hostile, killing all but one of the venturers. The lone explorer escaped back to the city and defensive measures were put in place to protect further threats.
The city expanded under the leadership of the former US military, building a self reliant ecosystem to support the ever growing population. Re-creating an annihilated infrastructure from scratch was no easy task and took several hundred years to complete due to lack of resources, expertise, and physical safety thanks to the now brutal surface conditions.
Communications relays were constructed and contact was finally reestablished with Luna which had been thriving on its own. The base had been successful in expanding their colonization efforts and boasted a population of over 40,000 citizens. The colonies had banded together and cooperated to survive on the celestial body while its home was destroyed. They had used their resources and access to existing technology to begin construction on the revolutionary Veritas Orbital Platform, Luna Orbit. This opened up new possibilities for Earth, providing them with a potential ally who could become a source of advanced technology and resources.
Lunar leadership offered to join forces with the survivors on Earth if they would dissolve their military leadership and assimilate, following all rules of law and governance they had established. Bastion couldn’t turn away from everything Luna had to offer but still wanted some control, so they accepted with one caveat. This new union would become the Sol Council with Bastion serving as its capital and political center.
Contact was finally made with the Martian colonies who had established several expansions. At nearly 25,000 citizens, they had overcome the harsh alien conditions and complete lack of assistance from Earth or its Lunar colonies. All things considered, they had done well for themselves and were extremely self-sufficient.
In 2715, raiders emerged for the first time trying to infiltrate Bastion. The city’s guards were put to the test and ultimately the Raiders were fought off. The incident prompted a review of Bastion's security measures and reinforced the need for better protection. With a population of this size, security forces inside and out the canyon were necessary. A new military organization was formed and @aegiswas created. They would operate on both Luna and Earth, but would be based on Veritas station.