Why did Shang Yang seduce the people of Sanjin, and why should the people of Sanjin be influenced by Shang Yang?

Induce the people of Sanjin to reclaim land in Qin State with real national strength: Qin State is vast and sparsely populated, while the neighboring Sanjin States have a small population. Shang Yang understood that "what the people want is also a farm house." "("Shang Junshu? In order to attract people "), he rewarded people from neighboring countries to farm in Qin, and Shang Yang gave these immigrants and families exemption from military service and engaged in a kind of specialized farming. In this way, these immigrants are responsible for the production of Qin, and Qin people can participate in military service and take turns to play, and there is still room for strength. This policy is of great significance, making Qin eat and drink enough and winning the war.