It could be called either a buffer or a wait state.
buffer state
Thailand
France and Great Britain
The buffer is in used is called as pinned buffer
A buffer state is generally interpreted as a state that lies between two hostile states
thailand served a buffer between british and french colonies
Thailand successfully convinced the British and French to leave his territory alone as a buffer state between their empires. During this era of diplomacy, the Thai kings also modernized the country, making the possibility of a violent confrontation between Western powers and Thailand less desirable for the numerically inferior Westerners.
Thailand
Thailand was seen as the "buffer zone" between France and Great Britain. Britain having India and France having south east Asia.
Which state was not a buffer zones between the North and the South
Mongolia is a perfect example of a buffer state, as it rests between China and Russia. A buffer state is housed between two large and hostile powers.