After the war with Teiro and the collapse of the Empire of the Seven-Pointed Star, Lanival divided the lands among the peoples. Some, like myself, believe the Leth Deriel truly belongs to Ilithi (and that it is only part of Zoluren because there was no Ilithi when the area was created), as the histories state that "To the Elves and Elotheans he left the ancient Ilithi lands". Certainly the fortress of Leth Deriel was a part of the Elven kingdom, and no where are there records clearly defining specific lines of division. Due to mechanics and ownership issues we'll probably never see a shift of provincial lines, but it's still a fun aspect to role-play.. we Elves are always having our lands taken from us ;)

~Lieutenant Kyrrian Sarantin, Ilithi Battering Rams.