YOSSI ALPHER is a former senior official in the Mossad and the former director of the Jaffee Center for Strategic Studies at Tel Aviv University. He currently coedits the bitterlemons family of Internet publications and writes a weekly Q & A on security issues for APN, which can be read at www.peacenow.org.

THE SIX-DAY WAR WAS UNDOUBTEDLY ONE OF THE MOST FATEFUL EVENTS in Israel's history as a modern state. Not just because we stunned the Arab world and conquered the territories-but because we held onto them. The occupation, particularly of the West Bank and Gaza, produced heavy fallout that we are still dealing with today: the rise of the Palestinian national movement and more recently the Islamists; the settlements; and the ills of sending first ourselves, then our sons and daughters and now our grandchildren to rule over another people.

It was our sense of vulnerability and lack of strategic depth that compelled us to take the battle to enemy territory and conquer it in this accidental war. But it was not foreordained that we remain occupiers for 40 years. I recall the atmosphere in IDF General Staff Intelligence, where I served as a first lieutenant, during the weeks that followed the end of the fighting on June 10, 1967. Based on Israel's experience dealing with what were then called the Great Powers in the aftermath of two earlier wars in 1948-9 and 1956, we assessed that yet a third intervention was imminent: Israel would be told in no uncertain terms to evacuate the territories it had occupied during the war. The ultimatum might be joint American-Soviet, or it could come from Moscow and be accompanied by veiled threats, naval maneuvers and the positioning of nuclear missiles.We would not be allowed to retain our conquests- whether as vital parts of the Land of Israel, bargaining chips for peace or what used to be called the legitimate spoils of war.

This was our only historical and political frame of reference for dealing with the global ramifications of the territorial outcome of the war. It explains why, within weeks, the Eshkol government annexed East Jerusalem. So hasty was that act that it ignored demography and even strategy in favor of short-lived tactical considerations: holding onto hills used by Jordanian snipers to shoot at Israeli Jerusalemites since 1948. The prevailing consideration was to preempt the anticipated Great Power ultimatum in the hope that Washington and Moscow would leave us this one small but symbolic triumph when they demanded we withdraw from the West Bank, Gaza, the Golan (then still called the "Syrian Heights") and Sinai. The older officers around me recalled David Ben Gurion proclaiming the "third temple" when we occupied Sinai in 1956, only to be compelled to turn around and withdraw. No one wanted to repeat that embarrassing event.

The ultimatum never arrived. Perhaps because the Arab states behaved so obstinately at Khartoum and said "no" to peace, even in exchange for territory.

Perhaps because in the prevailing Cold War atmosphere, Washington was as intoxicated with the IDF's triumph as was the average Israeli. Perhaps because the Soviets saw in the Arab setback, which their own policy mistakes had helped generate, a new opportunity to deepen their political and military penetration into the Arab heartland in Egypt, Syria and Iraq.

So my wife and I joined the celebration.We took our baby, who was born on the fifth day of the war, and toured Gaza and Nablus, the Jordan Valley and the Golan, the Temple Mount and Sinai. Slowly our government, left to its own devices, began very cautiously testing the waters of territorial aggrandizement: open borders; a proto-settlement in Hebron; a return to the Etzion Bloc; a kibbutz on the Golan. No one objected strongly, not even the Palestinian residents of the territories, who had never known a day without occupation. Yes, there were warnings, but few attempts to compel our compliance. And yes, when you read the now declassified protocols of Israeli Cabinet meetings from 1967- 68, here and there someone voices concern over the demographic consequences of holding onto the territories. But no one acted on those muffled warnings.

The rest is very messy history: settlements and settlers, war and intifada, withdrawals from Sinai and eventually Gaza, Palestinian terrorism and jihadi Islam. In one case, negotiations with Egypt, we were able to bargain a major portion of the 1967 conquests in return for peace, thereby seemingly justifying having held onto the territories-but only after a bloody and traumatic war in 1973. The Yom Kippur War may at the national level have somewhat reduced our conceit and reordered our priorities. But it also spawned Gush Emunim with its messianic settlement madness.

It would be convenient to blame the superpowers of the day for not intervening back in 1967, demanding our withdrawal and saving us from ourselves. Left to our own devices, a country barely 19 years old and flush with victory but still surrounded by enemies, we had to make our own decisions about the territories. And we made some bad ones, or so it seems in retrospect. Yet had we withdrawn, would things necessarily have been better without the settlements and the occupation? Would we still have made peace with Egypt, which after all was based on the territories-for-peace formula? Would we at least have avoided the Yom Kippur War? Would the PLO have come to Oslo in 1992-93 were it not for the impact of rampant Israeli settlement expansion? Might not the Palestinian national movement have ended up, with Syrian and Iraqi help, taking over Jordan and expelling our natural allies the Hashemites?

We can't relive the history of the past 40 years. We can only try to learn from it. Here are four lessons to ponder.

One clear conclusion we can draw is that, from the standpoint of Israel's survival as a Jewish and democratic state, the settlements in the West Bank, Gaza and the heavily populated Palestinian areas of East Jerusalem were a strategic mistake of catastrophic proportions. Another is that a thriving, coherently democratic Jewish state, however compact, constitutes far better "strategic depth" than the West Bank. Then, too, while our leaders back then made some bad decisions, our leaders today appear for the most part to have far less strategic understanding and fewer leadership capabilities.

Finally, not all subsequent strategic developments were caused by those six days back in 1967: the existential threat to Israel posed today by Iran and militant Islam derives far more from our very existence than from our misguided occupation of the West Bank.