The Council of the League of Nations approved the mandate terms for Palestine and for Syria and Lebanon. These documents turned wartime occupations into an international legal framework for governing former Ottoman lands. They set the stage for borders to be negotiated with the new Republic of Turkey and among the mandate territories themselves.
Greece and Turkey signed a convention at Lausanne to carry out a compulsory exchange of populations based mainly on religion (Greek Orthodox from Turkey; Muslims from Greece, with certain exceptions). Although centered on the Aegean region, the deal was part of the broader Lausanne settlement that aimed to reduce cross-border minority disputes. It reflected how state-building and border-making in the former Ottoman space often went together with forced migration.
Turkey and the Allied powers signed the Treaty of Lausanne, which recognized the boundaries of the modern Turkish state and replaced earlier post–World War I plans. Turkey also formally gave up claims to its former Arab provinces, a key step that cleared the way for the mandate borders in the Levant to be treated as permanent international frontiers. Lausanne left some border questions unresolved, especially around Mosul, but it set the main framework for post-Ottoman borders.
After France and Italy resolved outstanding issues, the League Council noted that the mandates for Syria and for Palestine had automatically and simultaneously entered into force. This is an important legal turning point: the mandate borders and administrations were no longer provisional arrangements. From this point, border negotiations with Turkey and among mandate units were conducted in the context of recognized international mandates.
The Treaty of Lausanne became legally effective after the required ratifications were deposited. This mattered for border-making because it confirmed that Turkey’s new international position—and the end of claims over Arab provinces—was now binding in treaty law. It strengthened the legal foundation for treating the Turkey–mandate frontiers as international borders rather than temporary lines.
Armed resistance to French rule escalated into the Great Syrian Revolt, challenging how the French mandate was administered across Syria. While not a border treaty, the revolt mattered for border formation because it pushed the mandate authorities toward tighter security, administrative reorganization, and clearer internal divisions. These pressures shaped how the mandate state units were managed within the broader borders established after Lausanne.
The League of Nations Council decided that the Mosul area should remain part of Iraq (then under British mandate), rather than joining Turkey. This decision tied border-making to international dispute resolution and to concerns about administration and security in a multi-ethnic region. It also increased pressure on Turkey, Britain, and Iraq to settle a definitive frontier by treaty.
Lebanon adopted a constitution that established the Lebanese Republic within the French Mandate framework. This was significant for border formation because it strengthened Lebanon as a separate political unit inside the mandate’s territory, reinforcing the idea of distinct successor states. Internal constitutional development and external borders worked together to make the post-Ottoman map more durable.
France and Turkey confirmed key sections of the boundary between Turkey and the French Mandate of Syria, including stretches aligned with the Baghdad Railway. This helped turn earlier, conflict-era lines into a more detailed and workable international border on the ground. It also illustrates how infrastructure (like railways) influenced where borders were drawn and how they were administered.
Turkey, the United Kingdom, and Mandatory Iraq signed the Treaty of Ankara to settle the Turkey–Iraq border and close the Mosul dispute. The agreement largely followed the League’s earlier decision, making the northern boundary of Iraq an internationally agreed frontier. This was one of the last major post-Ottoman boundary settlements touching the wider Levant region’s northern and northeastern approaches.
By mid-1926, the main international border disputes left open at Lausanne in this region had been addressed: the mandates were in force, Mosul was settled by treaty, and the Syria–Turkey boundary had received additional confirmation. This stabilization did not end local tensions, but it made the new borders harder to reverse through diplomacy. The Levant’s post-Ottoman borders now rested on both League decisions and bilateral treaties.
Treaty of Lausanne and subsequent post‑Ottoman border settlements affecting the Levant (1922–1926)