For a variety of conflicting reasons, the political leaders of Syria in January 1958 asked Nasser for a union between their two countries. Nasser was skeptical at first and then insisted on strict conditions for union, including a complete union rather than a federal state and the abolition of the Baath (Arab Socialist Resurrection) Party, then in power, and all other Syrian political parties. Because the Syrians believed that Nasser's ideas represented their own goals and that they would play a large role in the union, they agreed to the conditions. A plebiscite was held in both countries in 1958, and Nasser was elected president. Cairo was designated the capital of the United Arab Republic. Nasser then visited Damascus, where he received a tumultuous welcome. Arabs everywhere felt a new sense of pride.

Several Arab governments viewed Nasser with less enthusiasm, however. The conservative monarchies of Saudi Arabia and Jordan saw his ideas as a potential threat to their own power. Nasser regarded these monarchs as reactionaries and as obstacles to Arab unity. The United States moved to strengthen these regimes as well as the government of Lebanon in an effort to offset the influence of Egypt.

The hastily conceived union of Syria and Egypt did not last long. There were too many problems to overcome: the two countries were not contiguous, their economies and populations were different, and the Syrian elite deeply resented being made subservient to Egyptian dictates. The deciding factor for the Syrian upper and middle classes came in July 1961 when Nasser issued the so-called "socialist decrees" that called for widespread nationalizations. This was followed by the elimination of local autonomy and a plan for the unification of Egyptian and Syrian currencies, a move that would deal the final blow to Syrian economic independence.

There was also resentment in the army that paralleled the resentment in civilian circles. On September 28, a group of army officers called the High Arab Revolutionary Command staged a successful coup and proclaimed the separation of Syria from Egypt. Nasser decided not to resist and ordered his troops to surrender. He blamed Syria's defection on "reactionaries" and "agents of imperialism."