The Second Empire, also known as the Cyrodilic Empire is the name given to the period at the end of the First Era and the start of the Second when all Tamriel bar Morrowind was ruled by a single native dynasty.
 Reman Dynasty
The Reman Dynasty was founded by Reman Cyrodiil after he defeated the Akaviri invasion of Tamriel at the battle of Pale Pass in 1E 2703. Until that point, Tamriel had been divided into several small kingdoms, but once Reman had brought the armies of Colovia and the Nibenay Valley together to defeat the invasion, he was able to unite all Tamriel's human inhabitants in the face of possible aggression from the Aldmer.
Although the Battle of Pale Pass established Reman as the leading power in Tamriel, many parts of the continent refused to acknowledge his rule. Valenwood was not subdued until 1E 2714. In 1E 2811, Cyrodilic forces defeated the last organized army of Argonians at the Battle of Argonia, and the following year saw Argonia admitted to the Empire as a province under the name "Black Marsh". The rest of the province was conquered piecemeal, with the whole area passing under Imperial control in 1E 2837.
The last war of conquest began in around 1E 2840 when Reman II began an attempt to bring Morrowind, the only province outside Imperial control, into the empire. Progress was slow, and the three living gods of Morrowind's Tribunal, Vivec, Almalexia and Sotha Sil proved to be extremely capable leaders. By 1E 2920, both sides were approaching exhaustion and after the Empire captured the fortress of Ald Marak, a truce was agreed to bring an end to the war.
In the aftermath of the battle, both Reman III and his heir, Prince Juilek, were assassinated on the orders of Potentate Versidue-Shaie, bringing an end to the Reman Dynasty and instigating the period of the Second Empire known as the Akaviri Potentate.
 Akaviri Potentate
The Akaviri Potentate is the name given to the period of the Second Empire after the assassination of Reman III and the end of the Reman Dynasty. Additionally, it is the title given to the rulers of Tamriel both during this period and during the earlier years of the empire.
Under the Remans, the emperor's chief advisor was called the Potentate. In the battle of Pale Pass, Reman I decisively defeated an Akaviri invasion but other events forced him to offer the defeated army amnesty in return for their service in his own army. This led to Akaviri influence in other spheres of life, and over time the position of Potentate was usually filled by one of the snake people. In the year 1E 2920, the Potentate Versidue-Shaie plotted to overthrow the empire. He contrived the assassination first of Crown Prince Juilek and then the emperor himself. On 22 Evening Star 2920, Versidue-Shaie declared that he was taking over the leadership of the empire but retaining his title of Potentate. In the same speech, he declared the end of the First Era and the start of the Second.
In order to suppress armies remaining loyal to the Remans, as well as the armies belonging to individual kingdoms seeking greater autonomy, Versidue-Shaie was forced to engage in a relentless series of campaigns that, by the year 2E 283, finally resulted in victory for his forces.. The cost of the campaigns was immense, resulting in the impoverishment of both the empire and its constituent kingdoms and in an effort to maintain order without the expense of a standing army, in 2E 321 Versidue-Shaie agreed to a proposal from his kinsman Dinieras-Ves that established what was to become known as the Fighters Guild.
In 2E 324, Versidue-Shaie was assassinated by the nascent Morag Tong and succeeded by his son, Savirien-Chorak. In turn, he was assassinated along with all his heirs on one night in Sun's Dawn 2E 430, bringing a final end to the Second Empire and signaling the start of the Interregnum.