This policy is known as COLONIZATION.
Colonization refers to the action of settling down among foreign indigenous people and establishing control over them. Politically, this action is usually carried out by powerful countries. The Europeans were able to colonize Africa, America and India.
A. east of the Mississippi River
China was itself an established empire and could not be conquered the same way as they did Africa and India.
What you are saying is basically equal to saying why not land in England (during that period) and turn everyone into slaves.
Since that is impossible, establishing spheres of influence allows major powers to break China from the inside.
The major powers of europe, Japan, and America ganging up on china during those days is the main reason behind China's firm foreign policy today.
Sovereign means C) ability of a country to control its own affairs and function independently. The definition of sovereign is "...the full right and power of a governing body to govern itself without any interference outside sources or bodies."
