Second Sphere Expansion

The Second Sphere Expansion marks the second dynamic period of expansion of the Tau Empire, pushing further into space and establishing over a dozen new septs from 018.M39-742.M41. During this time, a legend arose from the Fire Caste, the greatest military thinker and strategist of his age, and perhaps of any other -- Commander Puretide. Towards the end of this period of expansion, the Tau Empire was brought into conflict with the Imperium of Man, who launched a crusade known as the Damocles Gulf Crusade to reclaim their long-neglected territory. This bloody campaign marked the end of the Second Sphere Expansion.

March of Conquest
The Tau have developed their own mode of timekeeping based on the annual cycle of T'au, a unit called a tau'cyr. Except on human planets that are still in the process of being subsumed, the Tau do not use the Imperium's dating system. However, for ease of translation, it has been done so here:

deadly plasma storms to ravage the planet, whose inhabitants survive by closing protective domes around their cities. Ork Warlord Garskrak and his invading army are lured into this deadly storm where they are utterly destroyed by the raging plasma radiation. into the fold. The Hrud and Arache reject the proposals and are driven out of the region. territory. It is a bloody campaign, which is finally stymied at Dal'yth Prime. The retreat of Imperial forces marks the end of the Second Sphere Expansion.
 * Second Sphere Expansion (018.M39) - The Ethereal Supreme, Aun'Wei of the Whispered Wisdom, gives the signal to begin the long-planned Second Sphere of Expansion. Aun'Wei's famous speech is well remembered, ending with "the nod that launched a million ships". With new advances in propulsion technology and an already established space empire, the second expansion is marked by more contact with aliens and larger wars.
 * A New Ally (053.M39) - The planet Vespid is absorbed into D'yanoi Sept. They had long been courted by the Water Caste -- but little was established save for crystal trade agreements. Within days of Ethereals' involvement, the Vespid Strain leaders convert wholeheartedly to the cause of the Greater Good.
 * N'dras Colonised (383.M39) - Despite Earth Caste reservations, from those who want to study inexplicable sensor readings, the planet N'dras is chosen by the Ethereal Council as the prime world of a new sept.
 * Steady Advancement (576.M39) - Improvements to anti-grav motors and new battlesuit technology (the T-series prototypes) help the Fire Caste complete the annexation of Tash'var Sept.
 * Mistaken Identity (876.M39) - War is declared upon the cruel raiders victimizing the new colonies of Ke'lshan. Believing they have tracked their foes down, the Tau instead destroy the Eldar Maiden World of Lilarsus. Further relationships continue to be strained.
 * Vio'la Triumphant (600.M40) - A massive Ork fleet invades Vior'la Sept but is defeated by a masterful campaign. Vior'la annually passes through a gap between its two stars, a time called the Trial by Fire. It causes
 * Mass Migration (896.M40) - The greatest Water Caste envoy, Por'O Dal'yth Kais Twi Lui'tan, better known as the Golden Ambassador, leads the effort to recruit alien worlds into the Tau Empire. During this period the Thraxians, Greet, and Formosians are welcomed
 * A Legend is Born (651.M41) - The birth of Commander Puretide, the pride of the Dal'yth Sept. His brilliant campaigns later conquer half a dozen star systems. Under his authority, the Tau envelop those who can be embraced, seize what can be conquered and obliterate those who defy the Greater Good.
 * The Once and Future Master (731.M41) - The elderly Commander Puretide is urged to view the new colonies across the Damocles Gulf before retiring. While inspecting a colonly, Puretide is wounded during a raid. Unable to walk again, the most revered of military leaders spends his remaining years atop Mount Kan'ji, on Dal'yth, where he is kept alive for many more decades. Only those who attain perfect scores at the Fire Caste academies are sent to sit at Puretide's hover-throne and learn his wisdom. Thanks to Earth Cast holographic technology, this tradition is still maintained, although few students are deemed worthy of receiving this high honour.
 * The Arkunasha War (733.M41) - A decade-long war in which a populous Tau colony is besieged by Orks. It is especially notable for the rise of the brilliant Puretide prtotégé named Commander Farsight.
 * The Damocles Gulf Crusade (742.M41) - The Tau Empire comes under attack by an armada of the Imperium's warships on a crusade to reclaim their long-neglected

Second Sphere Expansion Septs
The Second Sphere Expansion of the Tau Empire began in 018.M39, under the orders of Ethereal Supreme Aun'Wei of the Whispered Wisdom. With new advances in propulsion technology and an already established space empire, the second expansion is marked by more contact with aliens and larger wars. Around 742.M41, the Tau Empire comes into conflict with the human Imperium of Man who launch the Damocles Gulf Crusade in order to keep the Tau's expansion into Imperial-controlled space in check. The retreat of Imperial forces marks the end of the Second Sphere Expansion. Of note are the settlement activities of the Fire Caste's Commander Farsight during this period:
 * Au'taal - Au'taal Prime is a a verdant and beautiful Sept, where only honoured heroes can retire.
 * N'dras For reasons known only to the Ethereals, this once thriving Sept has largely been abandoned. Its remaining inhabitants are regarded as unstrustworthy, quick-tempered, and of a brooding countenance.
 * Ke'lshan - Situated near the Perdus Rift, this sept has suffered many invasions and is less trusting of aliens than other Tau. The Ke'lshan fleet and Fire caste forces are only recently back to full strength after their clashes with Hive Fleet Gorgon. Tau from this Sept have grown mistrustful, solemn, taciturn, unfriendly and sometimes openly hostile to alien races.
 * Elsy'eir - A densely populated Sept with many moons orbiting its prime world, most of which are mined for the valuable ores used in the construction of battlesuits. This Sept is known for its poetry and artwork. Its citizens are considered intellectuals and well-respected for their creativeness by other Tau. The Earth Caste is dominant on Elsy'eir.
 * Tash'var - A frontier sept, those of Tash'var have been subjected to frequent Ork invasions and pirate raids. As a result, its people have become tenacious and hardy.
 * Vash'ya - Known as the world "between spheres" the Sept was settled near the end of the Second Sphere Expansion, as it took a long period for the Earth caste machines to make the air breathable. Major Air caste fleets and many defence platforms are docked around the sept world.
 * T'olku - T'olku is known for its rnany large Ethereal temples, as well as the alien institutes, where many alien ambassadors are brought to be instructed in the ways of Tau culture and society before being assimilated back into their respective homeworlds.