You need to complete the focus "Return of the Sultan" in the Turkish Focus Tree. First time I did it the achievement did not pop and I thought I needed to get Greece. Second time I did the same thing and it popped. If it doesnt pop for you after researching the focus you gotta restart unfortunately.
*Civil war Tip*
When the civil war pops off they will always spawn in Trabzon and Western Turkey. Just have troops near both areas and micro manage. I start with Edirne and than Trabzon leaving Western Turkey for last.