Much of the world seems riveted by the question of whether Israel will attack Iran in order to destroy or at least delay its development of a nuclear weapon. This contingency is seen in Israel as an existential threat as articulated in one form or another by Iran's leadership including a reference to Israel as a "cancerous tumor" made by the Supreme Leader on February 3, 2012. The November 2011 report of the International Atomic Energy Agency removes the last shred of doubt with respect to the intentions of Iran towards its nuclear program. This, in turn, has mobilized the European Union to elevate its sanctions regime to include a boycott of Iranian oil. The United States has also been strengthening its sanctions regime with the addition of these steps taken against Iran's economy.
As a sovereign nation, it is Israel's decision to think about what steps it must take to defend itself against a nuclear Iran – a danger viewed by many as a grave threat to the Arab world, Europe, the United States, and most of the world.
Examining Israel's history seems to lead in opposite directions as to how we can expect Israel to respond to the existential threat posed by a nuclear Iran. (Keeping in mind the dangers of comparing historical scenarios disparate in time, country, technology and subsequent history.)
In 1967, Egypt's President Gamal Abdel Nasser precipitated a crisis with Israel and created a casus belli by closing the international Straits of Tiran to Israeli shipping, which was an economic lifeline for Israel. This siege was an act of war accompanied by not-so-subtle radio speeches proclaiming the "liberation of Palestine" and other threats hurled against Israel. (Earlier in the 1960s, Egypt had worked to develop missiles capable striking Israel, which Israel obstructed by assassinating the former Nazi scientists directing the program.)
For two months, Israel sought every possible international intervention to prevent war in the context of President Johnson's cryptic formulation that "Israel would not be alone unless it went it alone." Indeed, then Israel Defense Forces Chief of Staff Yitzhak Rabin noted: "I wanted it to be recorded for history that before acting, we did everything we could to find a diplomatic solution." Israel's forbearance in the face of the extreme provocation ended with the realization that no other country would assist Israel in the lifting of the siege. Israel's preemptive attack on Egypt soon followed on June 5, 1967, and the Six Day War with Israel's great victories over Egypt, Syria and Jordan changed the map of the modern Middle East, but sadly did not bring about the peace and recognition by its Arab neighbors that Israel has always sought. For the authoritative history of the Six Day War, I highly recommend Ambassador Michael Oren's Six Days of War: June 1967 and the Making of the Modern Middle East.
The Yom Kippur War of October, 1973 cast Israel in a much different position as it awoke to the near certainty of a surprise attack on two fronts from Egypt and Syria. The Six Day War left Israel dangerously over confident towards the military capability of the Arab world despite its massive rearming by the Soviet Union and the casualties suffered by Israel during the War of Attrition in 1970 with Egypt. Israel's intelligence services completely discounted the possibility of war even as the preparations for an Egyptian Suez canal crossing and the mobilization of the Syrian army could scarcely be hidden. (Indeed, Jordan's King Hussein traveled secretly to Israel to warn of the impending attack.) Only 24 hours before the attack, when Israel's top agents in London were provided information from an individual impeccably sourced, did Israeli intelligence admit the obvious.
Unlike 1967, though, Israel did not launch a pre-emptive strike but rather absorbed the first blow with the confidence it could repel the two-front invasion while gaining the political high ground by having not responded until attacked. This decision nearly proved fatal.
After suffering heavy losses, Israel eventually regained its military equilibrium only with the assistance of a massive American arms airlift. After many bloody battles, Israel expelled the Syrians from the Golan Heights and Mount Hermon and moved even closer to Damascus. Meanwhile, the Israelis conducted their own cross Suez Canal operation and trapped the Egyptian Third Army while gaining a bridgehead in Egypt proper.