When the first reports emerged Thursday that Hamas leader Yahya Sinwar was dead, Israeli Defense Minister Yoav Gallant posted a verse from Leviticus on X: “You will pursue your enemies and they will fall before you by the sword.”

Israel achieved a resounding moment of triumph when Sinwar’s death was confirmed several hours later. The architect of Hamas’s savage Oct. 7, 2023, attack on Israel is gone, and his death symbolizes Israel’s renewed military dominance across the Middle East. But a caution: Israel killed three Hamas leaders who preceded Sinwar without destroying that movement, so any victory announcements are premature.

Prime Minister Benjamin Netanyahu proclaimed that the “day after” has arrived in the Middle East, even as he warned that the war against Israel’s enemies would continue. He seemed to offer amnesty and safe passage out of Gaza to Hamas supporters if they disarmed and handed over the Israeli hostages. That’s a laudable idea but not an effective rescue plan.

It was a day of vindication for Netanyahu, who over the past year has gone from the abysmal failure of Oct. 7 to the military equivalent of running the table. Hamas’s forces have been crushed in Gaza. Hezbollah has been decapitated in Lebanon. And Iran, which Israeli leaders often describe as “the head of the octopus,” has been unable to strike back effectively. But despite Israel’s military success, Netanyahu has failed to prepare for what he knows lies ahead.

Sinwar’s life and death underlines why it will be so hard to create postwar stability in a tiny strip of land where more than 40,000 Palestinians are dead and 90% of the population have been driven from their homes.

For 50 years, Gaza has been a place of smoldering rage. That anger gave birth to Hamas in 1987. Sinwar had the perverse genius to mobilize that fury into a disciplined and devious fighting force that attacked Israel on Oct. 7 in what Netanyahu called the worst event for the Jewish people since the Holocaust.

Sinwar was schooled for violence. A superb profile of him by David Remnick published by the New Yorker in August described how Sinwar allegedly buried prisoners alive, poured burning oil on their heads and decapitated them with a machete. He created a theater of cruelty similar to the extreme violence of the Islamic State.

Israeli security forces arrested Sinwar in 1988 for his killings of Palestinian informants and sentenced him to life in prison. A less disciplined man would have gone soft, but Sinwar learned Hebrew, studied Israeli books and newspapers and began dreaming of revenge. He also wrote a novel from prison in Beersheba, published in 2004 with the title “The Thorn and the Carnation.” The book was a thinly disguised account of his own education in violent resistance, written to inspire others, “from the Gulf to the ocean, indeed, from the ocean to the ocean,” as he wrote.

Sinwar confessed his ambitions to an Israeli dentist who helped diagnose and treat what might have been a fatal brain tumor. Remnick interviewed the dentist, who recalled what now seem eerily prophetic comments by Sinwar. “We are ready to sacrifice twenty thousand, thirty thousand, a hundred thousand… After twenty years, you will become weak, and I will attack you.” Hamas’s Oct. 7 assault came precisely 20 years after Sinwar made that boast.

Sinwar was released in 2011 as one of about 1,000 Palestinian prisoners traded to free a single Israeli hostage, Gilad Shalit. The next year, he traveled to Iran to meet with Qasem Soleimani, the head of Iran’s Quds Force, Remnick reports. Sinwar became head of Hamas in Gaza in 2017; he slowly began assembling the arsenal for his eventual Oct. 7 foray into Israel and building the underground labyrinth of tunnels into which Hamas would escape when Israel mounted its retaliation, leaving Palestinian civilians aboveground to take the blows.

With Sinwar’s death, Israelis and Palestinians must yearn for a cease-fire and the return of the Israeli hostages. A deal has been carefully prepared by U.S. mediators, under which Israel would release at least 1,000 Palestinians — more than 100 serving life sentences — in exchange for the Israeli captives. This unbalanced swap was meant to appeal to Sinwar. Israel might not want to offer such generous terms with Sinwar gone.

“Our big project” is the name Sinwar and his commanders gave to their plan to burst through the Gaza fence on Oct. 7 and massacre Israeli soldiers and civilians. He hid the details for more than two years by pretending that Hamas wanted peace and prosperity in Gaza. “We can be like Singapore, like Dubai,” he told one of Remnick’s sources. Netanyahu swallowed Sinwar’s lie and nearly choked on it.

When Netanyahu says the war isn’t over yet, we should take him at his word. But that “day after” is ahead, and if Israel doesn’t prepare wisely for it, a new generation of Sinwars might be coming, too.