structural:expansion, quality:correction
United Arab Republic

Despite his popularity with the people of the Arab world, by mid-1957 his only regional ally was Syria. In September, Turkish troops massed along the Syrian border, giving credence to rumors that the Baghdad Pact countries were attempting to topple Syria's leftist government. Nasser sent a contingent force to Syria as a symbolic display of solidarity, further elevating his prestige in the Arab world, and particularly among Syrians.

As political instability grew in Syria, delegations from the country were sent to Nasser demanding immediate unification with Egypt. Nasser initially turned down the request, citing the two countries' incompatible political and economic systems, lack of contiguity, the Syrian military's record of intervention in politics, and the deep factionalism among Syria's political forces. However, in January 1958, a second Syrian delegation managed to convince Nasser of an impending communist takeover and a consequent slide to civil strife. Nasser subsequently opted for union, albeit on the condition that it would be a total political merger with him as its president, to which the delegates and Syrian president Shukri al-Quwatli agreed. On 1 February, the United Arab Republic (UAR) was proclaimed and, according to Dawisha, the Arab world reacted in "stunned amazement, which quickly turned into uncontrolled euphoria." Nasser ordered a crackdown against Syrian communists, dismissing many of them from their governmental posts.

On a surprise visit to Damascus to celebrate the union on 24 February, Nasser was welcomed by crowds in the hundreds of thousands. Crown Prince Imam Badr of North Yemen was dispatched to Damascus with proposals to include his country in the new republic. Nasser agreed to establish a loose federal union with Yemen—the United Arab States —in place of total integration. While Nasser was in Syria, King Saud planned to have him assassinated on his return flight to Cairo. On 4 March, Nasser addressed the masses in Damascus and waved before them the Saudi check given to Syrian security chief and, unbeknownst to the Saudis, ardent Nasser supporter Abdel Hamid Sarraj to shoot down Nasser's plane. As a consequence of Saud's plot, he was forced by senior members of the Saudi royal family to informally cede most of his powers to his brother, King Faisal, a major Nasser opponent who advocated pan-Islamic unity over pan-Arabism.

A day after announcing the attempt on his life, Nasser established a new provisional constitution proclaiming a 600-member National Assembly (400 from Egypt and 200 from Syria) and the dissolution of all political parties. Nasser gave each of the provinces two vice-presidents: Boghdadi and Amer in Egypt, and Sabri al-Asali and Akram al-Hawrani in Syria. Nasser then left for Moscow to meet with Nikita Khrushchev. At the meeting, Khrushchev pressed Nasser to lift the ban on the Communist Party, but Nasser refused, stating it was an internal matter which was not a subject of discussion with outside powers. Khrushchev was reportedly taken aback and denied he had meant to interfere in the UAR's affairs. The matter was settled as both leaders sought to prevent a rift between their two countries.

With the establishment of the United Arab Republic, the United States under President Eisenhower attempted to build better relations and initiate a rapprochement between the two countries, contrasting with the previously cautious stance of the American government towards Nasser. In particular, Nasser sought American assistance in his ideological cold war with Abdel Karim Qasim in Iraq and his ideology of Qasimism, which conflicted with Nasser's pan-Arab nationalism. However, due to major ideological differences, no significant long-term working relationship developed between Nasser and Eisenhower.