As we approach next month’s 50th anniversary of the 1967 war, we should not forget one of the enduring lessons learned from the run-up to the conflict.Namely, that agreements need to stand on their own merits and cannot be based on abstract international guarantees about the future. This idea was seared into Israel’s consciousness in May 1967. This painful lesson reinforced the Zionist ethos of self-reliance.Menachem Begin would later famously say: “There is no guarantee that can guarantee a guarantee.”On May 22, 1967, Egypt’s president Gamal Abdel Nasser closed the Straits of Tiran, a critical blow to Israel which relied on oil imports from Iran. Israel believed it had received a guarantee from the international community in 1957 that it would reopen the Straits if Nasser again closed them, as he had in 1956.After the Suez Crisis (Sinai Campaign) of 1956, prime minister David Ben-Gurion conceded in principle to withdraw from the peninsula, but requested several assurances before Israel could move ahead: Among the assurances he sought were that the Straits of Tiran wouldn’t be blockaded again, and that Israeli ships would have access to the Gulf of Aqaba and the Israeli port at Eilat. He also sought assurance that the UN Emergency Force (UNEF) in Sinai couldn’t be withdrawn just due to the sole demand of the Egyptians.President Dwight Eisenhower felt Israel was obligated to adhere to the UN resolution and withdraw, and could not put forward conditions for a pullout. At the same, he acknowledged, it had legitimate concerns. To square this circle in March 1957, he offered Israel a text known as an aide-mémoire through the State Department, which stated that: “no nation has the right forcibly to prevent free and innocent passage in the Gulf and through the Straits giving access thereto,” and that “the United States, on behalf of vessels of United States registry, is prepared to exercise the right of free and innocent passage and to join with others to secure general recognition of this right,” explicitly stating that blocking the straits is unacceptable. It implied but did not state that the US would be willing to use military means to back up its words.In a letter to Ben-Gurion following the aide-mémoire, Eisenhower wrote that Israel “will have no cause to regret” its decision to withdraw. Ben-Gurion conveyed to Eisenhower that he “saw freedom of navigation in Straits and Gulf of Aqaba as more or less assured.” In wake of Nasser’s move on the Straits, prime minister Levi Eshkol dispatched foreign minister Abba Eban on a whirlwind trip to Paris, London and Washington, to see if the international community would re-open the Straits, and avert war.However, Eban faced a changed political context from a decade earlier. Charles de Gaulle’s France was now making up with the Arab world in the aftermath of the French exit from Algeria, and was no longer the pariah that it was in the 1950s. De Gaulle conceded to Eban that the commitment to keep the Straits of Tiran open had been made. As Michael Oren writes in his Six Days of War, de Gaulle then declared, “that was 1957,” adding “now was 1967.” President Lyndon Johnson was preoccupied with Vietnam and his aides had to scurry to Eisenhower’s retirement residence in Gettysburg, Pennsylvania, to find out what had been promised.Johnson’s chairman of the Joint Chiefs of Staff, Gen. Earle Wheeler, did not like the British idea of a “regatta” or a group of ships from different countries to sail through the Straits, forcing Nasser to re-open them.When asked what if Egypt fires on the US in the event it forces it way through the Straits in such an instance, “it means war,” Wheeler declared. The regatta idea fizzled.However, the notion that international guarantees are not ironclad should not be confused with the thinking that Israel should only rely on force. The peace treaty between Egypt and Israel of 1979 and the peace treaty between Jordan and Israel of 1994 have withstood enormous regional and bilateral shocks in the last few decades.Critics derided each treaty as merely a cold peace. However, these agreements have paid major peace dividends for Israel.In the period after the 1973 war, US official figures estimated that Israel devoted half of its gross national product to military spending.On that percentage basis, this would mean that Israel would spend close to $150 billion per annum today. In fact, Israel’s military spending is less than $19b., according to the London-based International Institute for Strategic Studies. (Of that amount, $3.1b. comes from the US with another $500 million supporting Israel’s missile defense. Starting in 2018, the US is committed to the figure of $3.8b.) The difference in the two figures is obviously enormous – a peace dividend equivalent of over $130b. for every single year. That spending instead goes for roads, schools, clinics and a myriad of other programs that have led to a skyrocketing in the quality of life for Israelis.Peace has also meant that bilateral military- security relationships between Israel and Egypt and between Israel and Jordan are at a high-water mark due to common threats from ISIS, Hamas and other jihadis.The bottom line is that properly constructed agreements have been hugely important to Israel’s security and have withstood the test of time. Agreements work that serve the interests of both parties.This is fundamentally different from general promises of international intervention from third parties in future crises where there is no contractual alliance. There were many factors contributing to the 1967 June war, and one such factor was that international guarantees of a decade earlier were ephemeral.When the political context changed for the external parties, the guarantees evaporated.To be fair, international guarantees and security arrangements are not the same thing. Should the lesson of 1967 preclude the prospects of NATO- or US-led security arrangements in the Jordan Valley down the road in the event of an Israeli-Palestinian breakthrough? The issue has become extremely theoretical for now due to a variety of reasons, including the enormous gaps on issues between Israel and the Palestinians and the overall instability of the Mideast during the post-Arab Spring era. Of course, there are myriad factors to consider, and an aide-mémoire from Eisenhower about a theoretical future scenario would be critically different from detailed, concrete, ongoing security arrangements where Israel would have to be able to act successfully by itself if these arrangements collapse.The vacillation in the run-up to the 1967 war still teaches an important cautionary lesson, illustrating where international guarantees utterly failed. If the chips are down, Israel needs to be able to defend itself by itself.David Makovsky is the Ziegler distinguished fellow at the Washington Institute for Near East Policy. He was part of the US negotiating team during Israeli-Palestinian talks in 2013-2014.