noun
buffer state
A country situated between two larger, potentially hostile powers, serving to reduce the risk of conflict.
その小国は大国の間に位置する緩衝国として機能している。
That small country functions as a buffer state between the major powers.
Compound of 緩衝 (kanshō, 'buffer, cushioning') + 国 (koku, 'country'). The term is a calque from English 'buffer state'.