Oct 14 Turkey and Armenia signed accords in Zurich on Saturday to establish diplomatic relations and open their border.
Here are some details of the troubled history between the two countries.
Turkey closed its land border with Armenia in 1993 in protest at Yerevan's backing for ethnic Armenian rebels fighting for control of Nagorno-Karabakh, a region of Azerbaijan populated mainly by ethnic Armenians.
Turkey is a close ally of Muslim Azerbaijan and the two countries share close cultural and linguistic ties.
Some 30,000 people were killed in the war, which ended in 1994 with Armenian forces occupying Nagorno-Karabakh and seven adjacent districts of Azerbaijan.
In the late 19th century, the Ottoman Empire's some 2 million Armenians began to assert nationalist aspirations.
Repression by Ottoman irregulars, mainly Kurds, led to the massacre of 30,000 Armenians in eastern Anatolia in 1894-1896. Several thousand more were killed in Constantinople in August 1896 after Armenian militants seized the Ottoman Bank.
As the Ottomans fought Russian forces in eastern Anatolia in World War One, many Armenians formed partisan groups to assist the invading Russian armies.
On April 24, 1915, Turkey arrested and killed hundreds of the Armenian intelligentsia.
In May, Ottoman commanders began mass deportation of Armenians from eastern Anatolia. Thousands were marched towards Syria and Mesopotamia and Armenians say some 1.5 million died, either in massacres or of starvation and exhaustion in the desert.
The Zurich accords call for the creation of a commission of international experts to study the events.
Armenia insists they should be declared a genocide. President Serzh Sarksyan said in a speech to mark Armenia's annual Genocide Day that securing international condemnation of the killings was a priority for his administration.
Ankara strongly rejects the "genocide" description, saying large numbers of both Christian Armenians and Muslim Turks were killed during the chaotic break-up of the Ottoman Empire. Use of the term genocide has led to court cases under a law which forbids insulting the Turkish state.
The accords signed in Zurich to normalise ties need parliamentary approval. The Turkish government has said it expects to send the accords to parliament next week but has not said when voting will take place. Turkey or Armenia could hold off on approving the protocols if domestic opposition grows.
Once they are approved the border is due to open within two months.
Turkish Prime Minister Tayyip Erdogan said on Sunday that parliamentary ratification would require Armenian concessions in its conflict with Azerbaijan.
Armenian President Serzh Sarksyan faces strong opposition from the influential Armenian diaspora. Azerbaijan, the region's oil and gas power, has reacted angrily, fearing it will lose leverage over Armenia in negotiations over Nagorno-Karabakh.
The presidents of Turkey and Armenia were due to attend a World Cup soccer match together on Wednesday in a show of unity meant to help defuse opposition.
Sources: Reuters/Dictionary of Twentieth Century History.