The Turians are known to be the most disciplined of the Council races. They have a very militaristic culture and have great knowledge of ships and weaponry. They became a Council race when they defeated the Krogan during the Krogan Rebellions by deploying a Salarian made biological weapon, the Genophage.
The Turians originated from Palaven, and are greatly regarded from their contributions of soldiers and ships to the Council Fleet. They are the creators of C-Sec.
There is still great mistrust and anger between the Turian and Human communities, although they are slowly beginning to accept each other. The two were jointly responsible for the creating the SSV Normandy.
 The Unification War
Although the Asari were the first species to use the Mass Relays to discover the Citadel, the Turians had already discovered several Mass Relays and expanded their empire across multiple systems. As the Turian empire expanded, many colonies were being created further away from the Turian homeworld of Palaven. Due to lack of communication, the leaders of these colonies started to distance themselves from the Turian Hierarchy (the Turian Government).
These Turians soon began to rebel against their Government. They wore facial markings to differentiate themselves from the Hierarchy and they would open fire on any Hierarchy ships that came close to their planets. This eventually led to a Civil War between the Turian Government and the Rebels. Unfortunately, the rebel planets couldn't match the power of the Turian Military. After years of fighting the rebels were left hanging on to just a dozen colonies. When the Turian Heierarchy considered them too weak to fight, their leaders were forced to surrender and pledge their allegiance to the Hierarchy.
Dispite bringing peace to the situation almost 2000 years ago, many modern day Turians still wear the face markings of their home planet to commemorate the attempts of their ancestors.
 Krogan Rebellion
During the Rebellion, the Turians were a new species to the Galaxy with a formidable Military behind them. They took the front line in the war against the Krogans while the Salarians tried to find a scientific way to end the War. They created a biological weapon known as the Genophage which infected every Krogan and meant that nearly every Krogan offspring would die in stillbirth. The Salarians were hesitant to use it because they knew it would eventually lead to Krogan extinction. However, when the Turians got hold of it they didn't hesitate to use it. In the years that followed, the Krogan continued to fight, until they realized that they were just speeding up the extinction process. They eventually surrendered and the Turians became the third race to join the Council for their help in the Rebellions.
 The First Contact War
The First Contact War was never a big deal to the Turians. It lasted only a few months and they lost around 700 Turian lives. When questioned about it, most Turians will refer to the war as the 'Relay 314 Incident' as they considered it nothing more than a minor policing matter.
However, this war was a major part of Human history. It was humanity's first encounter with an Alien species and it was their first war to be fought in space. It all started when the Humans were trying to activate Mass Relay 314. This Mass Relay was shut down by the Citadel Council after the Rachni Wars and it was considered illegal to re-activate it. However, the Humans were unaware of the Citadel laws and when the Turians spotted them trying to activate the Relay they opened fire on the Human ships. Only one of the five ships returned to the Human settlement of Shanxi.
Out of all the Citadel species, the Turians were the only ones with any real military power, so they were surprised when the humans responded by destroying multiple Turians vessels. The Turians hit back by invading the human planet of Shanxi. Ashley Williams' great grandfather General Williams was the commander of Shanxi when he infamously surrendered. The Turians believed they had wiped out most of the human forces, however they would be proved wrong when a Second Human Fleet headed towards Shanxi. The Turians had underestimated the Humans military power and were caught off-guard by the second attack. As a result, they were quickly disposed of and Humanity soon took back Shanxi.
As the Turians were preparing for a full-scale war against the Humans, the incident started to pick up attention from other systems and the Citadel Council quickly stepped in to bring peace to the situation.