The Druids are an ancient lineage of Goa'uld , once ruled by a nameless Goa'uld, known only as "Eldest ". This earned them the name "Eldest Ones" or "Followers of Eldest". When war broke out between the Olympians and the Titans , the Druids were a smaller third faction that vowed for control of the galaxy. Due to their small numbers they relied on stealth and sabotage, but a week into the civil war, they seemed to simply disappear from the galaxy.
In reality, the Druidic Council cut off their planet from the galaxy, and entered a state of hibernation, leaving satellites in orbit that would prevent any sensor readings of their system and prevent any hyperspace travel into their system. Their stargate, however, was allowed access from one planet only--Chemosh . This was done because they were waiting for the one who betrayed them, Selvans, to return.
Something happened on Chemosh to Selvans and the other Druids, such that Gaia, Eldest's queen, said that she would not wish it upon any of her children that they had to return to Chemosh.</span>
The galaxy then forgot the Druids, until they were awakened by the return of Selvans to Genesaria . Since the death of Eldest, Selvans now rules the Druids.
History from Selvans' Point of View: http://w11.zetaboards.com/Stargate_Apocalypse/topic/7660291/1/
When the Druids regained contact with their Goa'uld brothers, they were shocked at how the system lords made use of humans and unas as slaves and workers. The Druids believe in the purity of the Goa'uld, and that human and unas slaves and workers make goa'uld society "impure", and that anything that is worked on by a human or unas is automatically inferior. This means that the only use for humans and unas in Druidic society is for basic household duties and as hosts.
Druid Goa'uld are also known for living without a host in the waters of a planet for long periods of time, sometimes even their entire life. However, when a Druidic army comes to a planet, their standard procedure is to immediately implant all but a few sentient life forms on the planet with Goa'uld, making themselves the only power on the planet. The surviving sentient forms (usually human or unas) are allowed to reproduce in captivity and work as household slaves, and as new hosts become available Goa'uld are implanted into them. This maintains a society with solely Goa'uld as a population.
The Druid Empire is comprised of a coalition of independent Druid Lords, but is ruled over by a council . The leader of this council is considerd to be the leader of all Druids, however each Druid Lord may leave the Druid Empire at any time they desire. In the past, the Druid empire has not been large enough for the Druid Lords to rule entire planets, but rather continents within planets. However, with the recent expansion, many Druid Lords, such as Pontus , Selene and Tian, do rule over entire planets or fleets.
The rules and decisions of the Emprie are made by the Druid Council, and once a decision is made, all the Druid Lords are informed. Once they receive word of a decision, they must either abide by it or they may leave the Druid Empire. New councilors are chosen every 3 years, and they are appointed by an anonymous vote from all of the Druid Lords.