There are three main factions in Elite: Dangerous; namely the Alliance, Empire, and Federation. The Empire and the Federation are the two main powers of the galaxy, and as a result, the Alliance was formed between numerous small and independent factions to increase their strength and defense against the two big factions.
The Alliance (full title, The Independent Alliance) was formed "out of a need for cooperation". Although it's member systems are very culturally different, they had a unifying goal- "to provide a stronger voice in the galaxy for it's member systems and ultimately to defend themselves against unwelcome attention from the big powers."
Politically, the Alliance's system has been described as a bit of a challenge due to the difference in cultures. However, militarily, it has been infinitely more successful. each nation contributes a portion of it's navy relative to their GDP to form the Alliance Defense Force; the six largest navy's admirals form the Council of Admirals. This council is able to act independently from the government without approval, and, throughout their history, there has been very little disagreement between the Admirals.
Although the Alliance Defense Force is composed of a myriad of navies, there is a strong sense of unity due to the Alliance emblem positioned next to the ships own navy emblem. This unifies the ADF, but heightens the rivalry between factions too.