Ever since he reincarnated, Mark was consistent on one thing, which is to develop grudges over the people with authority.
Likewise, there's also an unpaid debt with the Mt. Hua sect. Back then, he decided to forget it as the leader of Mt. Hua is a legendary realm expert (8-circle) and he doesn't have the strength to contend against him.
He expected it would take months or even years to achieve the strength enough to crush that entire sect but his growth accelerated at a rapid pace, and now that he could afford to showcase his enmity, Mark didn't hesitate to act.
Of course, he wasn't just acting on his feelings. To bring Shang Fu down, Mark planned to increase the dependency of the Imperial Palace on his firearms and other weapons.
However, just selling the weapons wasn't enough. Mark wanted to leave Shang Fu without any powerful and wealthy allies. His allies should turn into his enemies. Only then, when he gets dethroned, no one would come to his help.