It’s based on some of the same sources describing historical economies of other countries/regions. There are a variety of sources accessible online that go into more detail, including the ones cited in the excerpt I’ve included below.
> India experienced deindustrialisation and cessation of various craft industries under British rule,[12] which along with fast economic and population growth in the Western world, resulted in India's share of the world economy declining from 24.4% in 1700 to 4.2% in 1950,[13] and its share of global industrial output declining from 25% in 1750 to 2% in 1900.[12]
Of course a nation with a high population will have a high GDP in a mostly agrarian society. Per capita, there’s no indication India was ever the richest. They did fall behind massively due to an inability to compete during industrialization though. The attached source even mentions deindustrialization started in the waning years of the Mughals. Due to industrialization, the West’s GDP per capita simply outpaced India and China significantly, to the extent western nations even had higher nominal GDPs.
> Of course a nation with a high population will have a high GDP in a mostly agrarian society.
It was more industrialised than many or likely most western countries at the time with more advanced and valuable crafts, so in relative terms this seems rather suspect as a reason for dismissal. The original claim in the GP comment was that it was "one of the richest", which seems more than plausible given that it was likely higher than average GDP per capita pre-global industrialisation.
> The attached source even mentions deindustrialization started in the waning years of the Mughals. Due to industrialization, the West’s GDP per capita simply outpaced India and China significantly, to the extent western nations even had higher nominal GDPs.
The article mentions the 18th century, which is when the East India Company began its campaign to take over more land and resources. There is a significant amount of evidence that the EIC and later the British systematically deindustrialised areas that they colonised [1], and it's thought that the European industrial revolution depended on this rebalancing. I agree that the West's GDP per capita outpaced India's as a result of that, and this massive reduction in wealth and resources was the original point.
There is some information here about the British East India company pretty much destroyed the Indian textile industry through tarifs and other measures. Turning Indian from a leading textile manufacturer into a (much less profitable) producer of raw cotton for Britain's mills:
> India experienced deindustrialisation and cessation of various craft industries under British rule,[12] which along with fast economic and population growth in the Western world, resulted in India's share of the world economy declining from 24.4% in 1700 to 4.2% in 1950,[13] and its share of global industrial output declining from 25% in 1750 to 2% in 1900.[12]
https://en.m.wikipedia.org/wiki/Economic_history_of_India