To understand the origins of arguably the most important of the Arab-Israeli wars, it is important to look at post-1956 changes in the Arab world, Israel and international politics. The war was a result of long-term developments in all three of these key areas, and their impact upon one another.

The origins of the Six-Day War lay in part in the outcome of the previous Arab-Israeli war.

The issues at the core of that 1956 War were complex, for many reasons: the participation of the UK and France, the indirect participation of the US and the Soviet Union, and the strategic objectives of the participants.

For Britain and France, the Suez Crisis marked one of the last stands of the European colonial powers in the Middle East. By the end of the war, the US and the Soviet Union were the two major external actors in the region —as they remained until the demise of the Soviet Union in 1991.

From an Arab-Israeli perspective, the origins of the 1956 War lay in the outcome of the 1948 War. Israel had been unable to translate its military success into a political victory — namely Arab recognition of Israel’s right to exist. Crucially, this failure did not change after Israel’s military victory in 1956. Put simply, two rounds of fighting did not resolve the conflict.

Between 1956 and 1967, while the Israeli-Egyptian border remained relatively quiet (mainly thanks to the stationing of the UN peacekeeping force to act as a buffer between the two sides) the Middle East continued to be extremely volatile. Increasing disputes and military skirmishes over the region’s limited water resources threatened to develop into major conflicts. The US struggled to find a resolution but did at least prevent the outbreak of a major war over the issue.

During this period, President Nasser of Egypt was the central figure in the Arab world, and he attempted to export his brand of Pan-Arabism to other Arab states. Despite Egypt’s military defeat in 1956, Nasser survived with his authority intact. His position within the Arab world had been enhanced as he was perceived as having stood up to Western imperial aggression.

Egypt’s military losses to Israel were compensated for by the Soviet Union, which rapidly rearmed its major Arab client to military levels that matched, or bettered, its pre-war levels.

Nasser’s honeymoon proved to be short-lived. Egypt soon found itself embroiled in the civil war in Yemen in which its armed forces were widely seen as having performed badly. With no easy exit strategy from Yemen, Nasser’s popularity both in Egypt and in the wider Arab world rapidly declined. There was an increase in social unrest at home over the failure of key parts of his economic programme. By early summer 1967 his popularity was at an all-time low.

At the same time, Israel fared little better. The country was punished by President Eisenhower for its part in the 1956 War. Forced to return all the lands it had conquered in the war, Washington was still reluctant to sell weapons to Israel. As a result, it was largely reliant upon France for conventional weapons and, along with Britain, for developing its nuclear programme.

Diplomatically the inter-war years were characterised by increasing Israeli isolation at the UN and by a feeling in Jerusalem that the support of even Israel’s closest allies could not be guaranteed.

At the start of the sixties, the public trial of Adolf Eichmann, the architect of the Final Solution, compounded the feeling among Israelis that their country stood alone, surrounded by enemies. Radio Cairo provided regular reminders that the aim of the Arabs was to drive the Jews into the sea.

Politically, the period saw the transfer of power from the members of the Second Aliyah such as David Ben-Gurion to the leaders of the Third Aliyah. Israel’s Prime Minister and Minister of Defence, Levi Eshkol, was attacked as lacking strategic military skills and for being over-reliant on the advice of the young chief of staff of the IDF, Yitzhak Rabin.

Splits within the Labour Zionist movement (primarily over the Lavon Affair of 1954) meant that other key political figures with greater military experience such as Moshe Dayan were not in the government. The performance of Eshkol and Rabin in the first part of 1967 had been far from perfect with Israel dangerously escalating military exchanges with Syria.

Internationally, in 1967 the Cold War was at its height. The US was slowly losing a war in Vietnam and the Soviet Union sought to push home an advantage over its enemy.

The extent to which Moscow was willing to cause trouble for Washington in the Middle East remains a hotly debated topic among historians. At the very least the Soviets wanted to provoke a crisis to further pressurise the Americans.

The long-term reasons for the Six-Day War lay in the relative weakness of Nasser, the Israelis and the US. Understanding the timing of the outbreak of the war remains controversial. Much of the debate centres upon three key questions:

1 Did the Soviet leadership want to start a major Arab-Israeli war or simply to cause a crisis?

2 What were the intentions of President Nasser; specifically did he want to go to war with Israel?

3 Did Israel receive an amber light (proceed, but with caution) from the US to launch its pre-emptive strike on the Egyptian airfields on 5 June 1967?

The crisis that proved the catalyst started in May 1967 when the Soviet Union sent a false intelligence report to Nasser warning Egypt that Israel was massing forces on its border with Syria. The motives for the report were complex, but for Nasser it provided a get out of jail card from Yemen. He swiftly ordered his armed forces into the Sinai and demanded that the UN peacekeepers stationed there be removed. These moves help rejuvenate Nasser’s popularity among the Arab masses.

What followed was a rapid escalation in the crisis as both sides prepared for war. Nasser’s two key moves were to close the Straights of Tiran to Israeli shipping (an act of war in the eyes of Israel) and to forge a united Arab military coalition against Israel.

King Hussein of Jordan was pressurised into joining forces with Egypt and the two countries signed a formal defence pact on 30 May.

There remains much debate as to Nasser’s exact intentions. For most Israelis, his actions were a direct threat that could only lead to war. Tellingly, after the war Cairo and Moscow blamed each other for the missteps that led to its outbreak.

In Israel, the single most important development was the establishment of a National Unity Government on 1 June, which included Menachem Begin and Gahal for the first-time. The most significant appointment was that of Moshe Dayan as Minister of Defence. Previously, Dayan had publicly indicated that he felt that there could be no diplomatic resolution to the crisis.

Many international observers took his appointment as a signal of Israel’s intention to go to war. Dayan was also known to favour a pre-emptive strike against Egypt to help secure a rapid Israeli military victory in a war that he saw as inevitable. Despite the intense efforts of Abba Eban, Israel’s Minister of Foreign Affairs, to find a diplomatic solution to the crisis, attention soon turned to whether the administration of US President Johnson would give Israel permission to launch a pre-emptive strike. Both the President and his Secretary of Defence Robert McNamara were known to be against such a strike.

Historians continue to analyse the resulting key meeting between McNamara and an Israeli official in which it was claimed that Israel was given an amber light to launch a pre-emptive strike. To his dying day, McNamara denied providing Israel with any such support and the publicly available minute of the meeting confirms the Secretary of Defence’s position. In Israel, however, a different spin was put on the position of the Americans and the Israeli Cabinet voted in favour.

As a result, the third major Arab-Israeli War started on the morning of 5 June 1967 when Israeli planes attacked Egyptian air bases. The Israeli aircraft achieved near total surprise and destroyed much of the Egyptian Air force on the ground. The planes had been left in the open, away from their concrete shelters. There was an element of luck, however, in the Israeli attack. Jordanian radar had picked up the Israeli planes and transmitted coded warnings to their Egyptian counterparts. The codes had just been changed and the Egyptians failed to decode the messages in time.

By the end of the first day the Egyptian Air force had all but been destroyed.

With its dramatic strike, Israel was assured of victory. Using its air supremacy, Israel’s ground forces determined the scale of that victory over the next five days. Major victories in the Sinai followed, as well as in the West Bank and, after heavy fighting, the Old City in Jerusalem fell to Israel.

Following an internal debate involving Dayan, Eshkol and Rabin, Israel decided to take the Golan Heights.

The Six-Day War changed Israel’s strategic position beyond recognition. Israel controlled lands that could be used as a buffer zone: the Sinai, the West Bank and the Golan Heights. Most emotively, Jerusalem was united under Israeli control, including the holy sites in the Old City.

An important feature of the new political map was the large numbers of Palestinians in the West Bank and Gaza Strip that came under direct Israeli military rule. For the first time, Israel became an occupying power.

Nasser suffered a humiliating defeat. He offered to resign in the middle of the war, but apparent popular support persuaded him to stay on. At the time of that offer to resign, Egyptians had no idea of the scale of their defeat.

After the war, once the picture became clearer, there were renewed calls for his resignation.

In Jordan, King Hussein paid a heavy price for entering the conflict and would not make the same mistake in the 1973 War.

Syria lost its ability to shell Israeli settlements from the Golan Heights, but its leadership vowed to return the Golan to Syrian control.

Significantly, for the first time Israel had bargaining chips to trade at potential Arab-Israeli negotiations that were expected to follow the ending of the war.

The reality, however, was very different as it soon became clear that, once again, Israel would be unable to rapidly translate a military victory into the key political victory of Arab recognition of Israel’s right to exist.

Read all our coverage of the fiftieth anniversary of the Six Day War' here

Neill Lochery is the Catherine Lewis Professor of Middle Eastern and Mediterranean Studies at UCL and author of The Resistible Rise of Benjamin Netanyahu (Bloomsbury, 2016).