The Treaty of Lausanne was a peace agreement signed in Switzerland on 24 July 1923. Simply put, it helped settle a conflict between the Ottoman Empire and the Allied Forces after the war. How did it do that, you ask? The Treaty of Lausanne returned Smyrna to Turkey, reversing the Treaty of Sevres.
Should you want to know, the Treaty of Sevres was responsible for taking Smyrna away from Turkey and gifting it to Greece. It also turned Syria into a mandated territory under French control. Around this time, the Bosphorus was also placed under the control of the League of Nations, which meant Turkey effectively lost control of the entrance to the Black Sea through the agreement.
So, the Treaty of Sevres essentially saw Turkey lose control of its former Empire, with some countries becoming independent and the remainder becoming British or French mandated territories. As you might imagine, the Turks were outraged by this, and nationalists led by Mustafa Kemal drove the Greeks out of Smyrna, resulting in the Treaty of Lausanne.