Nocturnus Clan

The Nocturnus Clan, also known as the Fourth Great Nation as well as the derogatory "Marauders", is a clan of Echidnae that formerly inhabited Sonic's world some 4000 or more years prior to the current games' timeline. In their prime, the clan had used their superior abilities and technology to attempt to conquer the world, and would have succeeded if not for their abrupt abduction and subsequent imprisonment in a realm known as the Twilight Cage. They are the primary antagonists in Sonic Chronicles: The Dark Brotherhood, where they attempt to free themselves of the Twilight Cage in order to continue their conquest.

Pre-Argus
Not much is known of the Nocturnus Clan before their rivalry with the Knuckles Clan. How the rivalry came about is unknown, though it was likely due to the Clan's development of advanced technology giving them a sense of God-like superiority over the opposing clan. In any case, they were better equipped than their rivals. They were responsible for the creation of the Gizoid model of android seen frequently throughout other Sonic Games.

Although a primarily peaceful race, much like the Knuckles Clan, a sect of their numbers wished for conquest, and utilizing their steeply advanced technology, they began a much more successful conquest venture than the Knuckles Clan. And they would have succeeded if not for the inconvenient (to put it lightly) occurrence of the Argus Event, in which their civilization was ripped from the ground beneath them and pulled into the Twilight Cage, where it remained for what amounted to over 4000 years on Sonic's world. This left the Nocturnus Clan split. Without leadership, the members who survived the event for eventually peter out entirely. Around the same time, the Chaos Disaster had occurred, dealing a heavy blow to the Knuckles Clan of echidnae as well.

Pre-Chronicles
The clan's conquest would not cease, even within the Twilight Cage. There were four other races imprisoned there as well, the Voxai, Zoah, N'rrgal, and Kron. The echidnas, lead by Imperator Pir'Oth Ix, had conquered and forced their cellmates into submission, effectively dominating the Twilight Cage. Additionally, they stole elements from the other races in order to further improve their technology and defenses to protect and retaliate against potential acts of treason or other such hostility.

During this time, they echidnas put their smartest minds to work, and would eventually come up with a method of temporary reprieve from the cage.

The Events of Chronicles
Once they had obtained a method of escape from the Twilight Cage, they immediately set about finding a method of permanent escape in order to continue their conquest and reclaim Sonic's world.