The source of the treasury was from the faction member. When the faction member killed a zombie, they would get one coin, and at the same time, the faction itself also got the same amount of coin.
Tang Empire managed to amass 17 million coins in the last two months. Of course, he used a few million to upgrade the smart base and also to sponsor his people to get an advanced class.
Li Na, Lu An, Zhang Mengyao, Cao Jingyi, and Zhao Zhong had used a total of 5 million coins for their class. On top of that, he also had to arm his people by buying them the gears from the General Shop.
He then checked his coins by opening the status screen. To his surprise, he had around 9 million. He felt weird by the number, this meant more than half of the treasury was coming from him.