India is the most populous country in the world. It was the first and so far only country to surpass the 2 billion mark.
Throughout the 20th century, India was a rather poor country. Until 2003, Pakistan had a higher GDP per capita than India. However by the end of the 2nd decade, Pakistan began experiencing financial troubles. At the same time, tensions between the 2 countries eased. In 2030, Pakistan's economy collapsed and joined with India.
In the 2030s, India underwent a massive construction boom similar to China in the 2010s. By 2040, India's GDP overtook China's; the latter saw its government replaced by the one in Taiwan. Unlike China, India did not suffer an economic downturn. The reason China suffered a downturn was because the economy was tightly regulated by the government for so long and then they made economic reforms. The people treated the stock market like a place to bet money. They simply were not used to this economic freedom and so China snapped back regulations but the economic growth slowed down.
By 2050, India rivaled the US in influence. America's GDP was the 3rd largest in the world but their military was far superior. India had relations with both US and Russia. Because of this, India meditated the cold war, in search of a peaceful resolution. After the 2nd Gulf War, India got its wish and the 2 sides, fearing the same fate as the middle east, reduced nuclear arms.
India holds a third of the world's GDP. Although its population is aging, robots have largely taken over the manufacturing industry. Mechanics, programmers, and engineers saw a large increase.
In the next coming decades however, the nations of Africa are expected to rival India, particularly the DRC, Tanzania, and Nigeria.
Literally every city is connected via hypersonic vactrains. Airports have been phased out in favor of spaceports.
Showing someone from the 2000s the Mumbai of today would be like showing someone from WW1 the Manhattan of the 2000s. With a population of 67 million, Mumbai is the 2nd most populous city in the world. A multi billion dollar (2016 value) barrier protects the city from flooding. Because of the many tall buildings, subways have taken the place of traditional railways, much like New York City.
Delhi's skyline is more humble than Mumbai's but still holds an impressive skyline.
The Delhi-Mumbai industrial corridor started out in the 20s as 6 cities between Delhi and Mumbai, connected via railway. As time went on, these cities grew and expanded. Nowadays, Delhi and Mumbai are connected in all but name. This industrial corridor has a population roughly equaling America's population a century ago (300 million).