How Goa became a part of India
Goa was a Portuguese colony even after Indian independence. They were in no mood to give it up.
At the fag end of the 15th century Vasco da Gama set out to India around the Cape of Good Hope. He reached Calicut and wanted to cut a deal with the Zamorin. The Zamorin looked at Portuguese merchandise and said he did not wish to trade with them. As he set out on his way back to Portugal he was blowback due to the monsoon winds and ended up on Anjadip Island off the coast of Karnataka and therefore discovered Goa.
Goa had been a Portuguese colony and one of the most important ports on the western coast of India.
Incidentally, they cut several deals on the western coast for lands and one of the pieces of land that the Portuguese had acquired north of Goa was a swamp. This swamp was handed over as dowry to King Charles II when he married Princess Catherine the Braganza of Portugal in 1661. That swamp was called bumbai by the locals.
At the time, the British had been exclusively operating out of Calcutta. Since they had just finished building Fort St. George in Madras, it took them some time to turn to the west coast where they eventually established a Fort in 1769.
Coming back to Goa, the Portuguese used Goa, Daman and Diu, and Dadra and Nagar Haveli as their colonies in India. At the time of Independence, there were too many issues to be sorted and engineering the exodus of the Portuguese was not high on the list. It was not until 1955 that Jawaharlal Nehru opened up discussions on diplomatic channels for Portuguese exit and the handover of Goa to India.
By this time, the French had agreed to hand over Karaikal, Pondicherry, Mahé, Yanaon and Chandan Nagar back to India.
Portugal at the time was under the dictatorship of António de Oliveira Salazar. Salazar had no intention of handing back the territory to India. He claimed that Goa was part of Metropolitan Portugal and not a colony.
After multiple diplomatic attempts to settle the matter, Indian patience ran out in 1961. On 11 December 1961, the Air Force, the Navy and the Army was mobilised to take over Goa. Two days into the assault Fort Aguada fell, while the Murmagao port was attacked from the sea. On the 18th of December 1961, the 3500 Portuguese soldiers stationed in Panaji surrendered despite the instructions to the contrary from Salazar.
At the same time, Daman and Diu were also attacked and wrested from the Portuguese.
Goa became a Union Territory of India. At the time Goa was considered too large to be a union territory but too small to be a state. It was eventually found viable enough to be a state and provided statehood on 30 May 1987.
It was not until May 1962 that the prisoners of war were repatriated. Even today any Goan born before the 11th of December 1961 can apply for Portuguese citizenship.
Portugal and India did not resume diplomatic relationships until 1974.