1. The fall of the Ottoman Empire is linked to European imperialism. The Ottomans weakened during years of isolation and when Europeans began to expand they were unable to defend against conquest. The empire joined Austria and Germany in World War 1 which was the last straw for the empire. Turkey is the main country of the old Ottoman Empire.
2. Imperialism and the Treaty of Versailles (ending WW1) created country lines that made no sense in regard to cultural differences. This led to current day ethnic conflicts and warfare. Britain and France also controlled many economic resources and changed the power structure which was in place prior to World War 1.
3. The old Ottoman Empire was divided into new countries after WW1 which began conflicts in the region over access to land, resources, and holy lands. After WW2 and the events of the war, Allied powers created Israel taking land from the Palestinians. This move has created lasting conflict in the region.