 The first <unk> invasions of Burma ( <unk> ) ( <unk> : <unk> <unk> <unk> – <unk> <unk> <unk> <unk> <unk> ( <unk> – <unk> ) ) were a series of military conflicts between <unk> Khan 's Yuan dynasty , division of the <unk> Empire , and the Pagan Empire that took place between <unk> and <unk> . The invasions toppled the 250 @-@ year @-@ old Pagan Empire , and the <unk> army seized Pagan territories in present @-@ day <unk> , <unk> and northern Burma to <unk> . The invasions <unk> in 250 years of political fragmentation in Burma and the rise of Tai @-@ Shan states throughout mainland Southeast Asia . 
