Olleather was a previously medling, but somewhat benevolent power in Toril, helmed by a parliamentary monarchy system. Arguments among members of parliament were usually heated, but not acrimonious.
All this changed with the arrival of Severin Silragin and the Cult of the Dragon.
Slowly, they amassed power in parlament, whispering promises of power and the chance to fulfill their worst impulses. Soon, the King died, and they chose the new ruler, a devotee of Severin. Severin wasn't far behind, a trusted advisor to the new king.
Since then, Olleather has become less tolerant and more and more hungry for land and power. With Arvandor's rise, they have set their sights on obtaining their technology, and subjugation the merrow and other sea races, seeing them as "lesser beings."