The plans of the King of the Sandpeople are still quite reliable. Shenghai Kingdom is not a kingdom of just one species but an integration of many different species. There are humans, Beastmen, and other races.
In fact, originally in the south of Shenghai Kingdom, indeed, there were some Sandpeople living. However, these Sandpeople did not join them voluntarily, but were captured during battles.
When everyone realized that Sandpeople were actually similar to normal people and even possessed stronger physical strength, Sandpeople became a suitable option for slaves. Yes, slaves, not as their people.
It was inevitable, mainly because Sandpeople would eat humans and even liked to eat their own kind, their survival law was fundamentally incompatible with conventional morals, unacceptable to humans, and even Beastmen and other species couldn't accept it.
However, since Sandpeople made good warriors and were inherently strong, Shaliya couldn't bear to give up on them.