The answer is indirect rule
This term does not accurately describe the method used by European countries to govern through local institutions and officials.
Indirect rule refers to the system where European colonial powers governed their colonies by utilizing existing local power structures and leaders. This allowed them to control large territories with minimal administrative costs and resistance.
A client state is a country that is economically, politically, or militarily subordinate to another more powerful country, but it does not specifically refer to the governance method used by European colonial powers.
The civilizing mission was a rationale for intervention or colonization, purporting to contribute to the spread of civilization, but it does not describe the governance method.
Direct democracy is a form of government in which all laws are created by a general vote of society, which is not relevant to the colonial governance context.
The answer is more efficient guns and rifles
While chemical warfare did become significant in the 20th century, it was not a primary advantage during the earlier periods of European colonization.
Steamboats did provide logistical advantages, but they were not a direct weaponry advantage.
Aerial transportation was not developed during the primary periods of European colonization, and aquatic transportation, while important, was not a direct weaponry advantage.
Bomb canisters on trains were not a significant factor in the weaponry advantage during the colonization period.
Europeans had more advanced firearms, such as breech-loading rifles and machine guns, which provided a significant military advantage over the indigenous populations they conquered.