After the rebellion at the end of the Sui Dynasty, the population of the Tang Dynasty was only about 33.7% of that of the Sui Dynasty, and the land was barren. The court and the people are very poor. The court doesn't even have money. Except for some foreign officials with meagre salaries, the court can only give Beijing officials and foreign officials fields as wages. The office expenses of various government agencies have to be obtained by renting "public land".

In short, the economic situation in the early Tang dynasty was: lack of labor, lack of money, a lot of land, very cheap.

International situation: neighboring countries have been crippled by two emperors of Sui Dynasty. You can use a slave hunting army to capture barbarian slaves. Take it to Datang to farm and raise horses. Sold to officials and the court. Not only is the profit high, but it can also raise horses for the court and prepare for war forces.