The First Contact War
In 2156, just eight years after the discovery of Prothean ruins on Mars, scientists had used the Element Zero found on the Prothean ruin to expand their spaceships abilities in space travel. Humans could now travel further into the Sol System than ever before. While exploring Pluto, the humans discovered that Charon, which was previously thought to be a moon, was actually a Mass Relay covered in ice. The Relay was activated in the same year it was discovered and propelled Humans into Galactic Space.
 The Mass Relays
The humans quickly stormed through the Galaxy, activating any Mass Relays they could find, creating numerous colonies and expanding the Systems Aliiance Military. They had been exploring the Galaxy for eight years without coming into contact with another species. Then in 2164, the humans were trying to activate a Primary Mass Relay known as Relay 314.
There are two types of Mass Relay in the Galaxy, a Secondary and Primary. Secondary relays link to multiple other relays over short distances, usually to other relays in Citadel Space. However, Primary relays can send a starship over hundreds of light years but it will only link to one other relay and you can never be sure where it is. The Rachni originally discovered and activated a Primary relay and found themselves in Citadel Space. This led to the Rachni Wars and almost wiped out all Citadel species. After the war Primary relays were deactivated and the Citadel Council made it illegal to try and activate one.
 Turian Contact
The Humans however, had no idea about Primary Mass Relays, the Citadel species or their laws. When a Turian fleet spotted humans trying to activate Relay 314, they opened fire, only one of the five human starships made it back to the nearest human colony, Shanxi (named after the Chinese Province).
 Invasion 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 at Shanxi when he infamously surrendered to the Turians. It destroyed his military career and Ashley will tell you that she believes the rest of her family have never been able to rise to the high ranks in the Systems Alliance because of the incident. 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, they were quickly disposed of and humans took back Shanxi.
 Peace Negotiations
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. This was when the humans first discovered there were many more species in the Galaxy and they had their own political power.
The First Contact War only lasted for a few months before peace negotiations were settled between the two species. 623 Human lives were lost in the battle with a slightly higher number of Turian deaths. It would create a bad reputation for humans in the Galaxy for decades to come and their is still a lot of bad blood between the Humans and the Turians.
To the Humans, the First Contact War was a major part of their history. It was the first contact with an Alien race and their first war fought in space. However to the Turians it was a minor policing matter and simply refer to the War as the 'Relay 314 Incident'
Notable Humans who took part in the First Contact War include David Anderson, Admiral Ahern, the Grandfather of Ashley Williams and the Grandfather of Navigator Pressly. Saren Arterius' brother was one of the Turians killed during the War, this could explain his hatred for the Human race.