Rise of the Ghurids

Duke of Ghur, 867 or 1066 - the wiki prefers Muhammad Abbaszde in 1066. Restart for decent stewardship/learning traits, then play the inside game twice: reroll perks into Meritocracy, Claim Throne your liege, and back it with marriage alliances and a claimant faction; later swear fealty to the Seljuks and repeat the trick at imperial scale, sieging county by county while the emperor's stacks starve. Between coups, fully control Ghur and Kabulistan with income buildings everywhere and a couple of mangonel regiments. Then paint the historical Ghurid borders. The wiki also suggests converting to Afghan culture for tribal elective law and repeated invasion CBs off the antagonistic house-unity stance.