The second Holocaust will not be like the first. The Nazis, of course, industrialized mass murder. But still, the perpetrators had one-on-one contact with the victims. They may have dehumanized them, over months and years of appalling debasement and in their minds, before the actual killing. But, still, they were in eye- and ear-contact, sometimes in tactile contact, with their victims.

The second Holocaust will be quite different. One bright morning, in five or 10 years’ time, perhaps during a regional crisis, perhaps out of the blue, a day or a year or five years after Iran’s acquisition of the bomb, the mullahs in Qom will convoke in secret session, under a portrait of the steely-eyed Ayatollah Khomeini, and give President Ahmadinejad, by then in his second or third term, the go ahead.

The orders will go out, and the Shihab III and IV missiles will take off for Tel Aviv, Beersheba, Haifa, and Jerusalem, and probably some military sites, including Israel’s half-dozen air and alleged nuclear missile bases. Some of the Shihabs will be nuclear-tipped, perhaps even with multiple warheads. Others will be dupes, packed merely with biological or chemical agents, or old newspapers, to draw off or confuse Israel’s anti-missile batteries and Home Guard units.

With a country the size and shape of Israel, an elongated 8,000 square miles, probably four or five hits will suffice: no more Israel. A million or more Israelis, in the greater Tel Aviv, Haifa, and Jerusalem areas, will die immediately. Millions will be seriously irradiated. Israel has about 7 million inhabitants. No Iranian will see or touch an Israeli. It will be quite impersonal.

Some of the dead will inevitably be Arab, for 1.3 million of Israel’s citizens are Arab and another 3.5 million Arabs live in the West Bank and Gaza Strip. It is doubtful whether such a mass killing of fellow Muslims will trouble Mr. Ahmadinejad and the mullahs. The Iranians don’t especially like Arabs, especially Sunni Arabs, with whom they have intermittently warred for centuries. And they have an especial contempt for the Sunni Palestinians, who despite their initially outnumbering the Jews by more than 10 to 1, failed to prevent the Jews from establishing their state or taking over all of Palestine. Besides, the Iranian leadership sees the destruction of Israel as a supreme divine command, as a herald of the second coming, and the Muslims dispatched collaterally as so many martyrs in the noble cause. Anyway, the Palestinians, many of them dispersed around the globe, will survive as a people, as will the greater Arab nation. Surely, to be rid of the Jewish state, the Arabs should be willing to make some sacrifices. In the cosmic balance sheet, it will be worth the candle.

A question may nevertheless arise in the Iranian councils: What about Jerusalem? After all, the city is the third holiest after Mecca and Medina, containing the Al Aqsa Mosque and the Mosque of Omar. Ali Khamenei, the supreme spiritual leader, and Mr. Ahmadinejad most likely would reply that the city, like the land, by God’s grace, in 20 or 50 years’ time, will recover. And it will be restored to Islam and the Arabs.

To judge from Mr. Ahmadinejad’s continuous reference to Palestine and the need to destroy Israel, and his denial of the first Holocaust, he is a man obsessed. He shares this with the mullahs: All were brought up on the teachings of Khomeini, a prolific anti-Semite who often fulminated against “the Little Satan.” To judge from Mr. Ahmadinejad’s organization of the Holocaust cartoons competition and the Holocaust denial conference, the Iranian president’s hatreds are deep and, of course, shameless.

He is willing to gamble the future of Iran or even of the whole Muslim Middle East in exchange for Israel’s destruction. No doubt he believes that Allah, somehow, will protect Iran from an Israeli nuclear response or an American counterstrike. He may well believe that his missiles will so pulverize the Jewish state that it will be unable to respond. And, with his deep contempt for the weak-kneed West, he is unlikely to take seriously the threat of American nuclear retaliation.

Or he may be willing to pay the price. As his mentor, Khomeini, put it in a speech in Qom in 1980: “We do not worship Iran, we worship Allah. … I say, let” Iran “burn … provided Islam emerges triumphant. …”

Israel’s deputy defense minister, Ephraim Sneh, has suggested that Iran doesn’t even have to use the bomb to destroy Israel. The nuclearization of Iran will so overawe and depress Israelis that they will lose hope and gradually emigrate, and potential foreign investors and immigrants will shy away from the mortally threatened Jewish state. But my feeling is that Mr. Ahmadinejad and his allies lack patience and seek Israel’s annihilation in their lifetime.

As with the first, the second Holocaust will have been preceded by decades of preparation of hearts and minds by Iranian and Arab leaders, Western intellectuals, and press outlets. All the messages have served to demonize Israel. Muslims have been taught: “The Zionists/the Jews are the embodiment of evil” and “Israel must be destroyed.” And Westerners were instructed: “Israel is a racist oppressor state” and “Israel, in this age of multi-culturalism, is an anachronism and superfluous.”

The build-up to the second Holocaust has seen an international community fragmented and driven by separate, selfish appetites — Russia and China obsessed with Muslim markets; France, with Arab oil — and America driven by the debacle in Iraq into a deep isolationism. Iran has been left free to pursue its nuclear destiny, and Israel and Iran have been left to face off alone.

An isolated Israel will prove unequal to the task. Last summer, Israel failed in a 34-day mini-war against Hezbollah, which thoroughly demoralized the Israeli political and military leaderships. Since then, the ministers and generals, like their counterparts in the West, have looked on glumly as Hezbollah’s patrons have been arming with doomsday weapons.

The Iranian program will present even a more complex challenge for a country with Israel’s limited conventional military resources. Learning from Israel’s destruction in 1981 of Iraq’s nuclear reactor, the Iranians duplicated and dispersed their facilities and buried them deep. Taking out the Iranian facilities with conventional weapons would take an American-size air force working round-the-clock for more than a month. At best, Israel could hope to hit only some components and delay the Iranians by a year or two.

In short order, therefore, the leadership in Jerusalem would confront a doomsday dilemma of deciding whether to launch a pre-emptive nuclear strike.

Israel’s leaders most likely will grit their teeth and hope that somehow things will turn out for the best. Perhaps, after acquiring the bomb, the Iranians will behave ‘rationally”?

But the Iranians will launch their rockets. And, as with the first Holocaust, the international community will do nothing. It will all be over, for Israel, in a few minutes.

Still, the second Holocaust will be different in the sense that Mr. Ahmadinejad will not actually see and touch those he so wishes dead. Indeed, there will be no scenes like that quoted in Daniel Mendelsohn’s recent “The Lost, A Search for Six of Six Million,” in which is described the second Nazi Aktion in Bolechow, Poland, in September 1942:

“A terrible episode happened with Mrs. Grynberg. The Ukrainians and Germans, who had broken into her house, found her giving birth. The weeping and entreaties of bystanders didn’t help and she was taken from her home in a nightshirt and dragged into the square in front of the town hall. There … she was dragged onto a dumpster in the yard of the town hall with a crowd of Ukraininans present, who cracked jokes and jeered and watched the pain of childbirth and she gave birth to a child. The child was immediately torn from her arms along with its umbilical cord and thrown — It was trampled by the crowd and she was stood on her feet as blood poured out of her with bleeding bits hanging and she stood that way for a few hours by the wall of the town hall, afterwards she went with all the others to the train station where they loaded her into a carriage in a train to Belzec [extermination camp].”

In the next Holocaust there will be no such heart-rending scenes.

Mr. Morris is a professor of Middle East history at Ben-Gurion University in Israel.