The growth of the Ottoman Empire in the 15th and 16th centuries brought Armenia, along with swathes of the Balkans, under Turkish control. Ottoman laws treated all non-Muslims as second-class citizens, meaning Christian Armenians faced restrictions, such as having to pay a special tax, set at punitive levels.
In the 19th century, demands for Armenian independence grew, but protests met with savage reprisals in 1894 and 1909.
The first Balkan war saw large parts of Bulgaria, Serbia and Greece escape Ottoman control, but not Armenia. In 1914, Turkey allied with Germany, aiming to use the chaos of World War I to retake its former territories.
When a brief campaign in the Balkans resulted in crushing defeat, it turned its attention to the Armenian population, which it accused of collaborating with Russia. By early 1915 it moved those Armenians conscripted into the Turkish army into labour battalions.
Having disarmed the population, it rounded up individuals, starting with the arrest of 250 prominent Armenians in Constantinople (now Istanbul) on 24 April, which is generally acknowledged as the start of the genocide.
Months later, Turkey passed laws allowing it to round up anyone it liked and confiscate their property. Up to 1.5 million Armenians died, either executed directly or dying in concentration camps. Armenia became independent in 1918 at the end of World War I, but was invaded by Russia in 1920.
It became part of the Soviet Union, while part of its territory went to Turkey. While Turkey acknowledges the killings, it does not recognise them as genocide. Most non-Turkish scholars disagree.