Europeans, the vast majority of Americans, and good people the world over are now backing Israel as never before — but for how long? What happens when Israel turns the full force of its ire at Gaza’s urban centers, where it is already bombarding Hamas targets on an unprecedented scale? 

Prime Minister Netanayhu reportedly told President Biden that Israel has no choice but to send troops into Gaza, even though a land invasion is sure to escalate and protract the war. The rare and nearly universal global sympathy for Israel is likely to abate as the scale of destruction and suffering in the Strip rises along with death counts. 

“I wish to thank the many world leaders for their unprecedented support,” Mr. Netanyahu said Monday in his first public speech since the start of the war against Hamas, which he compared to the ISIS terrorist group. He especially thanked Mr. Biden, who, in a show of support, sent United States Ship Gerald Ford, an aircraft carrier, to back Israel. Mr. Netanyahu said that since Saturday he had worked endlessly to “shore up international support.” 

Yet, Mr. Netanyahu also vowed in his speech to do to Hamas “just as the enlightened world did to ISIS.” At the end of the war, he said, “all our enemies will know that it was a terrible mistake to dare and attack Israel.” Any place where Hamas resides, he added, “will turn to rubble.”     

The Hamas attack, in which a country once perceived as invincible was turned into a victim of unspeakable atrocities, including at least 900 dead in one day, has shocked outsiders. Solidarity with Israel was expressed in many once-critical quarters, with the country’s blue and white flags displayed on public buildings at European capitals and American cities.

“The scale of terror and brutality against #Israel and its people is a turning point, there can be no business as usual,” the European Union’s commissioner for neighborhood and enlargement, Oliver Varhelyi, wrote on X, announcing a suspension of $730 million in EU development aid to Gaza. 

On Monday, the United Nations secretary-general, Antonio Guterres, expressed his “utter condemnation of the abhorrent attacks by Hamas,” leaving more than 900 Israelis dead and thousands injured, and more than a hundred hostages having been kidnapped. “Nothing can justify these acts of terror and the killing, maiming, and abduction of civilians,” he said. 

Yet, what happens once Israel moves to offense from defense? The Israel Defense Forces announced Monday a call-up of 300,000 reservists, its largest such draft in decades. In televised interviews, IDF pilots say that their mission is “very different” from past Gaza operations.

“The gloves are off,” one pilot told Channel 11 news. As Mr. Netanyahu indicated, air attacks are expected to intensify significantly, perhaps accompanied by a land invasion. IDF instructions, reportedly, are to pay much less attention than in previous operations to incidental civilian casualties.    

Accordingly, Mr. Guterres said he is “deeply alarmed” at an already high death toll at Gaza. “While I recognize Israel’s legitimate security concerns, I also remind Israel that military operations must be conducted in strict accordance with international humanitarian law. Civilians must be respected and protected at all times,” he warned.  

Israelis are aware that world sympathy may be short-lived. Yet, most urge the IDF to conduct no-holds-barred military action in order to demolish Hamas’s ability to rule Gaza and to attack Israel militarily from there in the future. 

“We need to flatten Gaza to the ground,” a former IDF commander of military planning, General Israel Ziv, told public broadcaster Kan Monday, adding, “we live in a neighborhood where our entire survival depends on deterrence, and deterrence has been eroded.” The world may criticize, he says, but unless Israel employs brute force in the aftermath of Hamas’s unprecedented attack, Iran, Hezbollah, and other enemies will increase their aggression.   

“I have ordered a complete siege on the Gaza Strip,” the defense minister, Yoav Gallant, said Monday, flanked by the IDF Southern Command brass at Beersheba. “There will be no electricity, no food, no fuel, everything is closed. We are fighting human animals and we are acting accordingly,” he said.

Mr. Netanyahu, in his speech, said that “divisions inside Israel are over,” and called for a unity government. Yet, an already apparent lack of public trust in the government may well erode further as the current international support weakens, and as second-guessing of the IDF strategy comes to dominate global commentary.