With onslaught of World War I, the Ottoman Empire and Russian Empire engaged during the Caucasus and Persian Campaigns, and the CUP began to look on the Armenians with distrust and suspicion. This was due to the fact that the Russian army contained a contingent of Armenian volunteers. On 24 April 1915, Armenian intellectuals were arrested by Ottoman authorities and, with the Tehcir Law (29 May 1915), eventually a large proportion of Armenians living in Western Armenia perished in what has become known as the Armenian genocide. There was local Armenian resistance in the region, developed against the activities of the Ottoman Empire. The events of 1915 to 1917 are regarded by Armenians, Western historians, and even some Turkish writers and historians like Taner Akçam and Orhan Pamuk, to have been state-sponsored and planned mass killings, or genocide.