Rome and Achaea had been allies since the Second Macedonian War fifty years prior, but tensions between the two polities had been building up over the previous few decades, primarily over Roman efforts to throttle Achaean regional ambitions, particularly the long-desired assimilation of Sparta into the league, and the taking of large numbers of Achaean hostages by Rome in the aftermath of the Third Macedonian War. Tensions rose dramatically in 148 BC, when Achaea defeated and finally subjugated Sparta; in the aftermath of this, Rome tried to cow the League into halting its expansionist ambitions, but a failure of diplomacy between the two sides led to war.