The Egyptian–Libyan War, also known as the Four Day War (Arabic: حرب الأيام الأربعة), was a short border war fought between Libya and Egypt that lasted from 21 to 24 July 1977. The conflict stemmed from a deterioration in relations that had occurred between the two states after Egyptian President Anwar Sadat had rebuffed Libyan leader Muammar Gaddafi's entreaties to unify their countries and had started to pursue peace negotiations with Israel in the aftermath of the Yom Kippur War in 1973. Soon thereafter, Libya began sponsoring dissidents and assassination plots to undermine Sadat, in which Egypt responded in kind to weaken Gaddafi. In early 1976, Gaddafi dispatched troops to the Egyptian frontier where they began clashing with border guards. Sadat responded by moving many troops to the area, while the Egyptian General Staff drew up plans for an invasion to depose Gaddafi.
Clashes along the border intensified in July 1977. On 21 July, a Libyan tank battalion raided the Egyptian town of Sallum. The Egyptian forces ambushed it and subsequently launched a large counter-attack, conducting airstrikes against Gamal Abdel Nasser Airbase and sending a mechanised force 24 kilometres (15 mi) into Libyan territory before withdrawing. Over the next two days, heavy artillery fire was exchanged across the border, while Egyptian jets and commandos raided Libyan locales. On 24 July, the Egyptians launched a larger raid against Nasser Airbase and struck Libyan supply depots. Under significant pressure from the United States to end the attacks, and attempts from President of Algeria Houari Boumediène and Palestine Liberation Organisation leader Yasser Arafat to mediate a solution, Sadat suddenly declared a ceasefire. Sporadic fighting occurred over the next few days as Egyptian troops withdrew across the border. Relations between the two countries remained tense, and, though a formal agreement was never reached, both upheld a truce and gradually withdrew their forces from the border. Gaddafi softened his rhetoric against Egypt in the following years but actively rallied other Arab states to isolate the country.
In the 1970s Libya, led by Muammar Gaddafi, began a determined foreign policy of promoting Arab unity. He consulted Egyptian and Syrian leaders on taking steps towards that goal. When Egyptian President Gamal Abdel Nasser, a leading proponent of Arab nationalism, died in September 1970, his successor, Anwar Sadat, took his place in the discussions. The negotiations culminated in the creation of the Federation of Arab Republics (FAR) in 1972, consisting of Libya, Egypt, and Syria. Though the FAR was instituted with broad goals for the consolidation of each country's militaries, laws, and foreign policies, only symbolic gestures of unity were ever adopted, such as the establishment of a common national flag. In the following months, Gaddafi aggressively campaigned for immediate unity with Egypt, while Sadat's interest in unification steadily declined. Sadat also took a personal dislike to Gaddafi, finding him an annoying and unfit leader.
One of Gaddafi's major foreign policy goals, shared by many in the Arab world, was the elimination of Israel. He hoped that the combined power of Libya's finances, backed by a profitable oil-based economy, and Egypt's large population and military strength, could be used to destroy Israel. On 6 October 1973, Egypt and Syria, without consulting Libya, launched a co-ordinated attack on Israel, initiating the Yom Kippur War. Though an Israeli counter-attack eliminated Egyptian territorial gains in the early stages of the war, Sadat agreed to open negotiations with Israel, seeking the return of the Sinai Peninsula to Egypt in exchange for a guarantee to not engage in further attacks on the country. Gaddafi was angered by the war's limited objectives and the ceasefire, and accused Sadat of cowardice, undermining the FAR, and betraying the Arab cause. Sadat responded by revealing he had intervened earlier that year to prevent Libya from sinking a civilian passenger ship carrying Jewish tourists in the Mediterranean Sea. Thereafter, Egyptian–Libyan relations were marked by frequent accusations against each country's leaders, and further discussions regarding the pursuit of unity were abandoned.
Unnerved by Sadat's peace policy, Gaddafi sought to increase Libya's role in Middle Eastern affairs. Bolstered by strong oil revenues, he began acquiring a significant amount of weapons from the Soviet Union. He also sponsored Egyptian dissidents such as the Muslim Brotherhood, armed Egyptian insurgents, and made plans to assassinate Sadat. The Egyptian President responded by supporting subversion in Libya—including the possible extensions of encouragement to plots to assassinate Gaddafi—and backing anti-Libyan groups in neighbouring Chad. In February 1974, Sadat told United States Secretary of State Henry Kissinger to encourage Israel to refrain from attacking Egypt in the event it went to war with Libya. In early 1976, Gaddafi deployed Libyan troops along the Egyptian border, where they began clashing with Egyptian border guards. In the summer, Sadat decided to take military action against Libya's provocations, moving two mechanised divisions—totaling 25,000–35,000 troops—to the border and transferring 80 combat aircraft to Marsa Matruh Airbase, Egypt's westernmost airfield. Alarmed by this sudden escalation, Gaddafi dispatched an additional 3,000–5,000 troops and 150 tanks to the border. On 22 July, Gaddafi ordered Egypt to close its consulate in Benghazi. For a time being, the situation remained tense as it appeared Egypt would invade Libya, but after several weeks of no major action by the Egyptians, it appeared to the Libyans that there would be no attack.
Most observers at the time argued that Sadat did not order an invasion because it would stress Egypt's faltering economy and distance it from the Soviet Union and the Arab states in the Persian Gulf, which were already displeased with his policy towards Israel and overtures to the United States. Diplomatic sources have posited that Sadat was determined to occupy the Libyan capital, Tripoli, and depose Gaddafi. Egyptian sources also reported that Sadat wished to demonstrate to the Soviet Union that Egypt was stronger than Libya, and that its government should not abandon good relations with Egypt in favour of Libya. American intelligence analyst Kenneth M. Pollack concluded that the reason Egypt did not attack Libya at the time was because its army was unprepared; Egyptian forces had never rehearsed an invasion of Libya, and lacked the infrastructure and logistics in the Western Desert to support such an operation. Nevertheless, the Egyptian General Staff made plans for an attack. Egyptian Minister of War Mohamed Abdel Ghani el-Gamasy stated that the Egyptian Army was preparing for conflict in the west, while Egyptian media declared that Gaddafi was planning to annex the Western Desert with aid from Cuba.
Gaddafi increased his political pressure on Egypt, while the Egyptians continued to stockpile supplies and concentrate forces along the border. In May 1977, the Soviets told Libya and other Arab countries that they had evidence that Egypt was planning to launch an invasion. The Libyans ignored the warning and left most of their units at low levels of readiness, despite continuing to engage in border clashes with Egyptian forces. By the early summer, Egypt had completed its preparations for war. The Egyptian Air Force transferred Su-20 and Su-7 fighter-bombers of the No. 55 Squadron and Mirage 5 strike aircraft of the No. 69 Squadron to Marsa Matruh Airbase and nearby installations in anticipation of conflict. Significant clashes occurred on 12 and 16 July, and on 19 July, Libyan forces engaged in a drawn-out firefight with the Egyptians while conducting a raid. The Egyptian government reported that nine of its soldiers were killed. Gaddafi organised a group of civilians to march from Libya to Cairo, the Egyptian capital, to protest Sadat's policy towards Israel in the hopes that they would be well received by the population. After Egyptian border guards halted the demonstration at the frontier, Gaddafi ordered his forces to raid the Egyptian town of Sallum.