The Eldeen Three
Druidism originated in Khorvaire sixteen thousand years ago when Vvaraak, a black dragon, foretold a great planar invasion. In order to aid the humanoids in repelling this invasion she taught the first orc druids of the bond between the three progenitor dragons as well as how to tap into that power and use it to seal gates to other planes. These original druids are still known as the Gatekeepers and continue to protect Khorvaire from invasions of aberrations from other planes.
Seven thousand years after Vvaraak trained the first Gatekeepers the invasion that was foretold took place as illithids and daelkyr overlords swarmed onto the Material Plane from a gate to Xoriat. The Gatekeepers were able to repel this invasion and thus save the humanoids from enslavement.
In -4,100 YK (4900 years after the Gatekeepers repelled the invasion) another great druidic tradition sprung out of The Eldeen Reaches. Deep in the ancient forests a great pine named Oalian was awakened. Oalian has since become the central influence in many of the Eldeen Sects of druidism including the Ashbound, the Wardens of the Wood, the Greensingers and the Children of Winter. Though each of these traditions have varying beliefs they all share a commonality in their reverence for Oalian.
Although the Eldeen Reaches often comes to mind when thinking of druids and druidism there are druids all across Khorvaire and indeed across Eberron and even in other planes of existence. Anywhere the wild calls one can find druids of every species. Druidism is common among the lizardfolk of Q’Barra as well as among the fey in Thelanis even the drow among the ruins of Xen’Drik hold to ancient druidic traditions. Whether these were also taught to them by dragons, or if the power was discovered through other means is not yet known.