Nehru's policy against Goa was indeed a violation of international law, although it must be admitted, Nehru did attempt negotiation, and the vast majority of Goans favored accession to the Indian Union -- indeed, it was condemned even by the United States. But China at the time actually fully supported his policies in the name of anti-imperialism.
"In the rest of India, people began demanding that Goa be liberated forcibly. In 1955, a satyagraha was launched by the communist and socialist parties for the freedom of Goa. When the satyagrahis entered Goa, the Portuguese opened fire, killing 20 Indians. Nehru imposed an economic blockade, but was not prepared to go further. He hoped that the popular movement in Goa and the pressure of world public opinion would force the hands of the Goan authorities.
It was in 1957, in a letter to Vinoba Bhave, that Nehru first hinted at the possibility of military action. The Goan question came alive when Portugal paid no heed to a UN resolution of December 1960 asking it to indicate when it would grant independence to its colonies in Asia and Africa. In December 1961, Portuguese soldiers in Goa fired at villagers.
Finding that his policy of patience and adherence to international ethics had not yielded results, Nehru decided to free Goa by force. Though advised by American President John F. Kennedy, British Prime Minister Harold Macmillan and UN Secretary-General U Thant to postpone action, Nehru made up his mind. On December 18, after a long-drawn fight against Indian troops, the Portuguese gave up resistance. The Governor General of Goa, Vassalo e Silva, signed a document of unconditional surrender."
https://www.thehindu.com/opinion/op-...le22339624.ece