During the 1950's the Arab world was becoming polarized between pro-Western forces and the Arab nationalist vision of Egypt's president Gamal Abdel Nasser. Syria was a leader of the nationalist camp. In 1954 a Syrian military coup led to the emergence of nationalist, leftist groups.
The most prominent of these was the Arab Baath Party, which had branches in other Arab states. Under the slogan "one Arab nation with an eternal mission," its goal was the creation of a united, democratic, socialist Arab republic. The Baath Party gained increasing influence in the government, army, and professional classes. In 1958 strong domestic agitation finally led to Syria joining Egypt in the United Arab Republic (UAR), with Nasser as president.
The creation of the UAR stirred up division in Lebanon. Muslim communities celebrated and demonstrated in the streets. Muslim delegations were sent to Syria to congratulate its leaders, who in turn invited Lebanon to join the UAR. Lebanon's ruling Christian community just as strongly wanted the country to remain independent. The divisions between the two communities broke out into a civil war in 1958, during which Syria extended military support to the Muslim nationalists. After the civil war, stability returned to Lebanon, and the Muslims achieved a greater role in politics.
In 1961 a military coup installed leaders who withdrew Syria from the UAR and reestablished its independence. Syria's departure was a blow to Arab unity and Arab military strategy against Israel. Syria was now isolated in the Arab world and less of a threat to Israel. In 1963 army officers established a radical Baath military dictatorship. The government's strong anti-Israeli hostility, reinforced by Soviet support, was motivated by Arab nationalism and rivalry with Egypt. Moreover, it was convenient to be able to redirect domestic pressure against an outside enemy, Israel.