From the Summary: "Since having its boundaries drawn by France after the First World War, Lebanon has struggled to define its national identity. Its population then included Christian, Sunni Muslim, and Shi'a Muslim communities of roughly comparable size, and with competing visions for the country. Seeking to avoid sectarian conflict, Lebanese leaders created a confessional system that allocated power among the country's religious sects according to their percentage of the population. Since then, Lebanon's demographics and political dynamics have shifted, exacerbating tension among groups. Sectarian divisions have stoked violence, such as during the 1975-1990 civil war, as well as political gridlock on issues that require dividing power, such as government formation. These dynamics are intensified by external actors--including Syria and Iran--that maintain influence in Lebanon by backing Hezbollah and its political allies. Other states, such as Saudi Arabia, have backed Sunni communities as part of a broader effort to curtail Iran's regional influence. The United States has sought to bolster forces that could serve as a counterweight to Syrian and Iranian influence in Lebanon, providing more than $2 billion in military assistance to the Lebanese Armed Forces (LAF) since 2006, with the aim of creating a national force strong enough to counter nonstate actors like Hezbollah and secure the country's borders against extremist groups operating in neighboring Syria, including those affiliated with Al Qaeda and the Islamic State."
CRS Report for Congress, R44759
Congressional Research Service: https://crsreports.congress.gov/