The border frontier's lower ranks of soldiers amounted to a total of two hundred thousand, teaching them all at once was unlikely.
Li Xiaobai selected a group of soldiers who appeared to be relatively smart to teach the first batch of the Spirit Realm Technique. Of course, what was taught was merely the most inferior version of the cultivation technique, which would only allow these soldiers to cultivate to the Qi Cultivation Spirit Refining stage. To go further, they would still need to find additional follow-up cultivation techniques.
But that was no longer Li Xiaobai's concern.
By having the soldiers who had learned it teach those who had not, efficiency greatly increased. The number of martial artists who learned the inferior version of the Spirit Realm Technique grew exponentially; in just over ten days, a full fifty thousand out of the two hundred thousand soldiers had learned this technique.