This refers to an administrative-not military-act of government in which one country seizes land belonging to another country or people

Annexation

Explanation:

Annexation is different from Conquest.

in conquest , we use our military force to make another country surrender and take over the control through force.

In Annexation, a country take control over another country through administrative/legislative method. Usually, this can be done by obtaining the support from the majority of the people who live in that other country. When most of the people wanted to join, the government will become more likely to legally hand over the control and become part of the union.