Mass Effect, Mass Effect 2 & Mass Effect 3
Roughly 1200 years ago, the turians were invited to join the Citadel Council to fulfill the role of galactic peacekeepers. The turians have the largest fleet in Citadel space, and they make up the single largest portion of the Council's military forces.
As their territory and influence has spread, the turians have come to rely on the salarians for military intelligence and the asari for diplomacy. Despite a somewhat colonial attitude towards the rest of the galaxy, the ruling Hierarchy understands they would lose more than they would gain if the other two races were ever removed.
Turians come from an autocratic society that values discipline and possesses a strong sense of personal and collective honor. There is lingering animosity between turians and humans over the First Contact War of 2157, which is known as the 'Relay 314 Incident' to the turians. Officially, however, the two species are allies and they enjoy civil, if cool, diplomatic relations.