There isn't a power in existence that dares to oppose the might of Qin River City. Melvin Jones quickly overpowered Sun and Moon City leading his forces.
"Master, there isn't anything of urgency. I have certain insights on cultivation and wish to retreat for some time." Peter Brown met Robert Lee and told him about his plans of closed-door cultivation.
It was quite common for a cultivator to suddenly seclude themselves, sometimes even for decades. Robert Lee was not surprised and after glancing at Peter nodded, "Alright, you can go cultivate, Qin River City's strength is now immense. We have successfully captured Sun and Moon City. I don't foresee too many issues arising."
Peter didn't choose to go into seclusion within Qin River City, as he would surely need to wield his Immortal power. Thus, Peter had to find a desolated place.