What concept refers to the policy of extending a nation’s authority over other countries?

The concept that refers to the policy of extending a nation's authority over other countries is known as imperialism. This term encompasses the various methods through which a nation might exert its power and control, such as through military force, diplomatic pressure, or economic influence. Historically, imperialism is often associated with the expansion of empires, where stronger nations establish dominance over weaker ones, thereby often exploiting resources and influencing local governments.

Colonialism is related but more specifically denotes the practice of settling and directly controlling foreign territories, which is a part of imperialism. Nationalism refers to the strong sense of pride and loyalty to one's own nation, often leading to the desire for self-determination and independence, rather than the domination of others. Protectionism is an economic policy designed to restrict international trade to protect domestic industries, which does not inherently involve the authority over other countries. Thus, imperialism distinctly captures the essence of extending national authority over foreign lands.