Final answer:
A state that is independent and free from external control is known as a sovereign state, which has the authority to govern itself and engage in international relations.
Step-by-step explanation:
In the context of international law, a state that is independent and free from all external control is referred to as a sovereign state.
A sovereign state is one that governs itself, independent of any foreign power, and has the full authority to engage in diplomacy, such as making war or peace, and forming treaties or alliances with other nations.
Vassal states, in contrast, retain some degree of internal autonomy but are subject to the dominance of another power.
Sovereignty is essential for a state as it enables the enactment and enforcement of laws and policies without external interference, which is foundational for a nation's ability to function and protect its interests.
Independence and statehood have historically been recognized by membership in organizations such as the United Nations, and the increase in the number of independent states over time, particularly after the decolonization movement, demonstrates the importance of sovereignty on the global stage.
correct option C) Sovereign state