World War I
Greece went into the war because its leader supported the Allied cause. Greece and Serbia had become independent, but many Greeks still lived in lands that had once been Greek but were now Ottoman. Having recently won the Balkan Wars, the Greeks wanted especially to control other land to the north that was under Bulgarian and Ottoman rule and so they declared war. The Ottomans killed most of the Greek Army as they tried to regain parts of the Ottoman Empire. Another war started when the Greeks bombed a train. The Ottomans swept the Greeks back into their own territory. From then on, the Greeks never again declared war, but the Ottomans had one of the largest armies in the world.