Sounds like a Malthusian situation. Constant internecine warfare shrinks the population, so the subsistence wage can go up and per capita increases; the Raj comes in, unifies India under a peaceful hegemon, and by the usual Malthusian logic of an increasing population (with no war to check it), per capita wages begin to fall. I notice one bump upwards in the wages comes in the 1850s, which is around the Sepoy Rebellion...