 After Aibak's death, the region became independent, with Lakhnauti as its capital, and Ali Mardan's successor Ghiyasuddin Iwaj Shah (alias Husamuddin Iwaz Khalji) styled himself as a sovereign Sultan.While Iltutmish was busy at the north-western frontier of his empire, Ghiyasuddin captured parts of present-day Bihar, and also extracted tribute from the smaller states of Jajnagar, Tirhut, Bang (in Bengal region), and Kamrup.Iltutmish's forces captured Bihar in the 1210s, and invaded Bengal in 1225.