The partitioning of a country against the will of the majority of its inhabitants violates its right to self-determination. The Twentieth Century produced several instances:
Ireland in 1922
India in 1947
Korea in 1948
Germany and China in 1949
Vietnam in 1954
Cyprus in 1974.
In Ireland, India and Vietnam, partition was imposed by the colonial power as a result of its “divide and rule” policy. In Ireland, the support for Ulster Unionism by the British Conservative Party caused the creation of Northern Ireland in 1921. Britain imposed separate electoral lists for Hindus and Muslims in India (1919), thereby starting the sectarian politics which culminated in the creation of the Muslim state of Pakistan in 1947. Vietnam was partitioned by France into a Communist northern state and an anti-Communist southern one in 1954. In other words, in each case the colonial power conquered a united country and wrecked it by creating two hostile states. The results caused warfare between India and Pakistan ( 1947, 1965, 1971, 1999 ), between North and South Vietnam (1965-1975), civil war in Southern Ireland (1921-3), and insurrection in Northern Ireland (1969-98).
The partitions of Korea and Germany were created by the rival occupying powers after the Second World War. The outbreak of the Cold War between the West and Soviet Union in 1948 meant that the latter established communist republics in its zones of occupation (North Korea and East Germany). Similarly, United States naval power prevented the mainland communist Chinese taking the island of Taiwan, to which the Nationalist Government fled, resulting in the creation of two rival Chinese states. All this could have been avoided by negotiation, as happened in Austria where the occupying powers all agreed to evacuate the country (which thus became a neutral state in 1955).
Cyprus was divided by Turkey’s invasion of the north coast in 1975 to protect its ethnic compatriots. Turkish Cypriots fled thither, and Greek Cypriots were expelled. The result is two rival governments in the North and South. Forty years of negotiations for reunification have proved abortive. Once a country is destroyed, it is very difficult to reunify it. It is, nonetheless, achievable. Vietnam did so by force of arms in 1975, after a ten year war costing three million lives. Germany did it peacefully, because the imploding Soviet Union was no longer able to sustain its ally, the (East) German Democratic Republic which then collapsed. North Korea’s attempt, however, failed and resulted in the Korean War (1950-53) in which five million perished.
The partitions of the Twentieth century were thus all disastrous. They helped minorities avoid “the tyranny of the brute majority” (as Jinnah, the founder of Pakistan, said), but the cure was worse than the disease.