Assam is the valley the whole region drains into. The Brahmaputra runs its length, braided and several kilometres wide in places, and everything organises around it — the tea gardens on the terraces above the flood line, the river islands, and the wet grassland that makes the state's wildlife possible.
That grassland is the reason Kaziranga holds roughly two-thirds of the world's greater one-horned rhino, along with wild buffalo, swamp deer and a tiger density as high as any protected area anywhere. It is also why the park shuts for five months a year: the monsoon puts much of it under water, and the animals move to higher ground.
The other Assam is the older one — the Ahom kingdom that held this valley for six hundred years and kept the Mughals out of it seventeen times, leaving the tanks and temples around Sivasagar. And Majuli, where the neo-Vaishnavite satras have been centres of dance, mask-making and manuscript for five centuries, on an island the river is steadily taking back.