Kolkata port in 1945. It was an important military port during WW2.By the early 19th century, Kolkata was split into two distinct areas — one British, one Indian, known as 'Black Town'. Even at the time, the poverty of the 'Black Town' shanties was considered shocking. The city underwent rapid industrial growth from the 1850s, especially in the textile and jute sectors; this caused a massive investment in infrastructure projects like rail roads and telegraph by British government. The coalescence of British and Indian culture resulted in the emergence of a new Babu class of urbane Indians — Asia's first middle class — whose members were often professionals, read newspapers, were Anglophiles, and usually belonged to upper-caste Hindu communities. Throughout the nineteenth century, a socio-cultural reform, often referred to as the Bengal Renaissance resulted in the general uplifting of the people. In 1883, Surendranath Banerjea organised a national conference — the first of its kind in nineteenth century India. Gradually Kolkata became a centre of the Indian independence movement, especially revolutionary organisations. The 1905 Partition of Bengal on communal grounds resulted in widespread public agitation and the boycott of British goods (Swadeshi movement). These activities, along with the administratively disadvantageous location of Kolkata in the eastern fringes of India, prompted the British to move the capital to New Delhi in 1911. The city's port was bombed twice by the Japanese during World War II. As food stocks were being diverted to feed Allied troops, millions starved to death during the Bengal famine of 1943.In 1946, demands for the creation of a Muslim state led to large-scale communal violence resulting in the deaths of over 2,000 people. The partition of India also created intense violence and a shift in demographics - large numbers of Muslims left for East Pakistan, while hundreds of thousands of Hindus fled into the city.

Over the 1960s and 1970s, severe power shortages, strikes and a violent Marxist-Maoist movement — the Naxalites — damaged much of the city's infrastructure, leading to an economic stagnation. In 1971, war between India and Pakistan led to the mass influx of thousands of refugees into Kolkata resulting in a massive strain on its infrastructure. In the mid-1980s, Mumbai overtook Kolkata as India's most populous city. Kolkata has been a strong base of Indian communism as West Bengal has been ruled by the CPI(M) dominated Left Front for three decades now — the world's longest-running democratically-elected Communist government. The city's economic recovery gathered momentum after economic reforms in India introduced by the central government in the mid-1990s. Since 2000, Information Technology (IT) services revitalized the city’s stagnant economy. The city has also experienced a growth in the manufacturing sector.