New Delhi, Jan. 12 -- India is entering the most consequential phase of its development since independence. Between 2026 and 2047, the year Independent India turns 100, its economy, population and cities will undergo transformations unmatched in scale. Managed well, this period could propel India into the ranks of high-income, innovation-driven economies. Mismanaged, it could see the country fall short just as its greatest demographic advantage begins to fade.

Three structural forces will shape India's future over the next two decades: rapid economic expansion, the maturing of its demographic profile and accelerated urbanization. Together, they create a narrow but powerful window for reform and execution.

Economically, India's momentum ...