 In 738 , <unk> , a vassal of <unk> , <unk> 's key ally in the south , switched allegiance to <unk> , defeated <unk> and gained its own independence . It appears that this was a conscious effort on the part of <unk> to bring about the collapse of <unk> 's southern allies . This upset the balance of power in the southern Maya area and lead to a steady decline in the fortunes of <unk> . 
