Cyprus became a part of the Ottoman Empire in 1571. So its population has been part Greek and part Turkish for quite a while. In the 19th century, Britain looked for a convenient outpost enroute to the Suez Canal and cut a deal with Turkey to declare the island a British protectorate in 1878: The Turkish formally refrained from their territorial claims and Britain would use the island as a base to defend the Ottoman Empire against the possibly aggressive Russians. In 1914, Britain fully annexed the island because Turkey joined the Central Powers in WWI.
Since the early 20th century, large parts of the Greek Cypriots wanted Cyprus to become a part of Greece but Britain didn’t want to let go.1 In 1950, the Orthodox church held an unofficial referendum among the Greek Cypriots in which an overwhelming majority voted to join Greece. The British ignored the vote and the Greek Cypriots threatened Britain to bring the case to the UN. The British then replied that Turkey should have a say, too, and Turkey answered that it would reclaim Cyprus in case its status changed. The Turkish Cypriots supported the status quo, too, but later on switched to the separation into a Greek and Turkish part.2
In the 1950s, both Greek and Turkish Cypriots established armed underground organisations to fight for their claims. However, both Greece and Turkey were already in the NATO by then and the US worried that their quarrels might hurt the southwest border of the alliance. Consequently, the US pushed for a compromise. In 1960, Britain granted Cyprus its independence on the condition that it could keep its airforce bases on the island. Greece and Turkey became guarantors to the new state and could station troops there.
Unfortunately, this was no solution to the inner-Cypriot tensions because every dispute between the Greek and Turkish Cypriots could now easily escalate to a confrontation of the Greek and Turkish military. The first serious tensions between the 77 percent Greek and 18 percent Turkish Cypriots arose in 1963 when the country’s first president (who was Greek) wanted to change the constitution. The Turkish were unhappy with his proposals as they would have made them a privileged minority. The disagreement provoked bloody disturbances and the UN sent a peacekeeping force which established a buffer zone between the predominantly Greek and Turkish parts. Turkey almost invaded the island but the US forcefully “persuaded” them not to.
Meanwhile, things went south in Greece when a military junta ruled it from 1967 to 1974. As a first result, unification became less popular among the Greek Cypriots. Second though, the junta helped Greek Cypriot officers to stage a coup against Cyprus’ democratic government. This prompted Turkey to invade. The Greek junta was overthrown three days later but Turkey continued with the invasion and brought 40 percent of the island under its control. The Greek Cypriots in these territories were dislodged and moved to southern Cyprus while Turkish Cypriots in southern Cyprus were forced to move north. Ever since, there have been negotiations to end the conflict but none were successful.
In 1983, the north unilaterally declared its independence as the Turkish Republic of Northern Cyprus. This region is de facto independent but only acknowledged by Turkey; the rest of the international community sees it as a part of the Republic of Cyprus. To put it straight, there are three countries on Cyprus: the acknowledged (Greek) Republic of Cyprus, the de facto Turkish Republic of Northern Cyprus, and the UK with two British Overseas Territories around its military bases.