A buffer state is a country lying between two rival or potentially hostile greater powers, which by its existence is thought to prevent conflict between them. Buffer states, when authentically independent, typically pursue a neutralist foreign policy, which distinguishes them from satellite states. The conception of buffer states is part of the theory of balance of power that entered European strategic and diplomatic thinking in the 17th century. In the 19th century, the manipulation of buffer states like Afghanistan and the Central Asian emirates was an element in the diplomatic "Great Game" played out between the British and Russian Empire for control of the approaches to strategic mountain passes that led to British India.