The agricultural situation in the medieval Northeast began to change from 13th century AD. Onwards. Brahmaputra valley under the Kacharis was acquainted with plough and wet rice cultivation. However, cultivation was predominantly shifting in nature besides gathering (of fruits, roots and herbs) and hunting-fishing activities. The subsistence economy of the region was not able to defend itself from the invading agriculturists.
Ahoms were basically an agricultural tribe and if the legend is believed they came to the valley in search of cultivable land. They subjugated the local tribes and established themselves in the extreme southeastern part of the valley. Ahoms originally belonged to Mongolia, China and are credited to have introduced wet-rice cultivation on a wider scale in the Brahmaputra valley.
Contemporary chroniclers noted sub-regional variations within Assam. Mughal chronicler Shihabuddin Talish remarked that even the foreigners were attracted by the flourishing wet-rice cultivation in Brahmaputra valley. On the other hand, Ralph Fitch in 1585 noted only the cultivation of silk, bamboo, cotton, cane etc., in the lower Assam. Compared to the valley, the hills practiced primitive methods of rice cultivation besides hunting and gathering activities. With little modifications the variations still exist.