The term "genocide" did not exist before 1944. It is a very specific term, referring to violent crimes committed against groups with the intent to destroy the existence of the group.
Part I: The Setting
The Ottoman Empire was an empire in turmoil and decline by the 20th century. Already inclined toward Germany due to economic ties, close relations between the two militaries, and compatible territorial ambitions for a war against Russia, the new Young Turk government concluded a secret military agreement with the German government on August 2, 1914, and formally entered the war on the side of the Central Powers on November 11.
Beating back an initial Russian invasion, Ottoman troops invaded the Caucasus (today: Armenia and Georgia), and sought to advance their military position into the Persian Empire (today: Iran). That winter, the Turks suffered a catastrophic defeat in the Caucasus, and another at the Suez Canal in a failed attempt to push the British out of Egypt. Russian troops invaded the Ottoman Empire, moving into the east Anatolian provinces of Trabzon, Erzurum, and Van (all of which had large Armenian populations). Great Britain and France attacked the Empire during the last week of April 1915 at Gallipoli, with the aim of knocking the Ottomans out of the war.
Part II: Armenians in Conflict Zones
Although the Ottoman Empire was predominantly Muslim, there were also significant Christian populations. In the eastern provinces, Armenian Christians made up 45% of the population.
Under pressure, Ottoman military chiefs pressed for the deportation of Armenians from the war zone on the grounds that they represented a potential fifth column (group within a country at war who are sympathetic to or working for its enemies) acting in enemy (Russian) interests. When challenged by the Allied Powers and the still neutral United States, Ottoman authorities explained the deportations as a precautionary measure.
In January 1915, the Russians routed Ottoman troops at the Battle of Sarakimis and the Ottoman 3rd Army lost more than half of its soldiers. Although Armenian soldiers in the Ottoman army generally fought loyally and bravely, Ottoman leaders chose to publicly blame the defeat on supposed Armenian traitors.
Part III: Forced Labor and Massacres on the Front
Retreating from positions in the Caucasus and in Persia in February–March 1915, Ottoman authorities executed populations viewed as potentially disloyal, leading some Armenians to take up arms in self-defense. When Russian troops invaded that April, some of these armed bands joined them. Reinforced in a suspicion that all Armenians were potential traitors, Ottoman commanders disarmed their own Armenian soldiers deployed on the eastern front and imprisoned them in forced-labor battalions.
As the Russians approached in April and early May, a majority of Armenian leaders urged compliance with the Ottomans and most Armenian civilians obeyed. Nevertheless, an armed group rose against the Ottoman garrison in Van and had seized control of the city by the time the Russians arrived on May 18, 1915. The Ottoman regime saw this insurrection as confirmation of a generalized Armenian disloyalty.
Part IV: The Forced Marches and Camps
Many victims include people killed in local executions that began in Spring 1915; others who died during deportations, under conditions of starvation, dehydration, exposure, and disease; and Armenians who died in or en route to the desert regions of the southern Empire [today: northern and eastern Syria, northern Saudi Arabia, and Iraq]. In addition, tens of thousands of Armenian children were forcibly removed from their families and converted to Islam.
Although we do not have reliable figures on the death toll, many historians accept that between 800,000 and one million people were killed, often in unspeakably cruel ways, or marched to their deaths in the deserts to the south