Modern Syrian–Lebanese relations were shaped to a great extent during the French Mandate. In 1920, France created two separate entities, proclaiming the State of Greater Lebanon and incorporating the coast, the Bekaa Valley, and the southern districts into the former Mount Lebanon. The legal separation was formalized by the Mandate documents of 1922, Lebanon’s 1926 Constitution, and the treaties of 1936. At the same time, supporters of Syrian and Arab nationalism continued to advocate the unity of historic Syria. In 1943, Lebanon adopted the National Pact, combining the country’s independence with its “Arab face.” After French and British troops withdrew in 1946, relations began to develop between two independent states with an inherited and incompletely demarcated border.
In the following years, economic and political differences between the countries grew. In 1950, after negotiations on common interests and a single currency failed, they completed a full customs and economic separation. During the 1958 Lebanese crisis, internal divisions in Lebanon and concerns about the influence of the United Arab Republic led to US intervention and a Syrian–Egyptian–Lebanese agreement reaffirming Lebanon’s independence. The 1969 Cairo Agreement legalized Palestinian armed activity from southern Lebanon, and in 1970 the Palestine Liberation Organization’s leadership moved there. This became one of the factors that led to the 1975 civil war between the right-wing Christian camp and the left-wing Muslim bloc allied with the PLO.
In June 1976, the Syrian army officially entered Lebanon at the request of President Suleiman Frangieh and a number of Christian politicians seeking to prevent a victory by leftist forces. In October of that year, Syria’s presence received Arab cover במסגרת the Arab Deterrent Force. After the Syrian–Christian alliance broke down in 1978 and Israel invaded in 1982, Syria reduced its area of presence to the Bekaa Valley and northern regions, while also supporting the creation of Hezbollah together with Iran. In 1987, Syrian troops returned to West Beirut, and the 1989 Taif Agreement provided for their redeployment to the Bekaa Valley. However, on October 13, 1990, Syrian forces seized East Beirut, overthrew Michel Aoun’s government, and established full control over the country.
The Treaty of Brotherhood, Cooperation and Coordination, signed in 1991, cemented Syria’s influence over Lebanese politics, personnel appointments, and foreign relations. In 1998, with Damascus’s support, Emile Lahoud became president. After Israeli forces withdrew from southern Lebanon in 2000, demands for the withdrawal of Syrian forces intensified. Bashar al-Assad’s regime pressured former Prime Minister Rafik Hariri and the opposition, contributing to the adoption of UN Security Council Resolution 1559 in 2004, which called for the withdrawal of foreign troops, the disarmament of armed groups, and an end to interference in elections. Following Hariri’s assassination in February 2005, the Cedar Revolution began, and in April the last Syrian soldier left Lebanon.
Syria’s withdrawal led to a victory for the March 14 Alliance, but tensions with Damascus persisted. The 2006 war and the May 2008 clashes deepened the confrontation between the March 14 forces and the March 8 bloc allied with Syria and Iran. In October 2008, Syria and Lebanon established official diplomatic relations for the first time since gaining independence. Saad Hariri’s visit to Damascus in 2009 was an attempt at reconciliation, but its results were limited. After the Syrian uprising began in 2011, Lebanon became divided over the conflict and received large numbers of refugees, while Hezbollah announced in 2013 that it was intervening militarily on the side of Assad’s government. The policy of non-intervention failed to isolate Lebanon from the war.
The border became a complex security and trading zone. In 2017, Operation Dawn of the Outskirts targeted the Islamic State and Jabhat al-Nusra, while in 2018 Syrian government forces restored control over a significant part of the border areas. Lebanon’s economic crisis and the US Caesar Act of 2019 disrupted trade and transit, while simultaneously expanding the illicit trade in fuel, goods, currency, and drugs. After Syria returned to the Arab League in 2023, limited contacts resumed on refugee and border issues. Following the fall of Assad’s regime on December 8, 2024, Syria’s new authorities declared their respect for Lebanon’s sovereignty. In March 2025, the countries signed an agreement on security coordination, border control, and the start of border demarcation. In 2026, officials continued exchanging visits, discussing the fate of prisoners, missing persons, and disputed sections of the border. However, security problems, smuggling, and regional interference remain.
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How did the historical concept of “Greater Syria” influence Syrian and Lebanese nationalists’ attitudes toward the border created by the French Mandate? — The idea of “Greater Syria” was based on the belief that Syria, Lebanon, Palestine, and Jordan formed a single historical and geographical space. Consequently, many Syrian nationalists regarded the border drawn by the French Mandate authorities after World War I as an artificial division. Lebanese nationalists, particularly supporters of an independent Lebanon, viewed that border instead as the foundation of the country’s sovereignty. This difference preserved mutual distrust and made the border issue part of a broader dispute over national identity.
Why did the 1969 Cairo Agreement become so important in strengthening the PLO’s role and subsequently changing the balance of power in Lebanon? — The agreement allowed the Palestine Liberation Organization (PLO) to conduct armed operations against Israel from areas of southern Lebanon and granted it substantial autonomy in the Palestinian refugee camps. Although Lebanon’s sovereignty was formally preserved, the state lost some control over the south of the country. The PLO became an independent military and political actor, and its presence heightened tensions among Lebanon’s communities and became one of the factors contributing to the civil war that began in 1975.
What role do disputed sections of the Syrian–Lebanese border, particularly in the Shebaa area, play today in relations between Damascus, Beirut, and Hezbollah? — The Shebaa Farms area is used by Hezbollah to justify continuing its armed struggle against Israel: the movement considers the territory Lebanese and maintains that it remains under Israeli occupation. The UN generally treats Shebaa as part of the Golan Heights, whose status is linked to the Syrian–Israeli conflict rather than viewing it as unequivocally Lebanese territory. Syria supports Lebanon’s position, but for a long time it did not formalize it through complete and unambiguous internationally recognized documentation. As a result, the dispute enables Damascus to maintain influence over Lebanese politics, while allowing Hezbollah to justify retaining its weapons. For Beirut, it remains an issue of sovereignty and diplomatic pressure on Israel.
Full version: Chronology of the Key Milestones in Syrian–Lebanese Relations