Operation Iron Swords was a large-scale military operation undertaken by the Israel Defense Forces in response to the deadliest terrorist attack in Israeli history, Hamas' Operation Al-Aqsa Flood offensive. Prime Minister Benjamin Netanyahu issued a formal declaration of war on Hamas in the aftermath of the Palestinian terrorists' surprise offensive, and Israel called up its reservists and assembled up to 350,000 troops for an operation with the stated goal of destroying Hamas and its capability to govern the Gaza Strip.
In preparation for an all-out assault on Gaza, Israel carried out airstrikes on the Gaza Strip, destroying the 11-story Palestine Tower (which housed Hamas radio stations on its rooftop), several buildings of the Islamic University of Gaza (used as training facilities by the Izz ad-Din al-Qassam Brigades), and other targets. On 8 October alone, Israel struck up to 426 targets, mostly leveling the town of Beit Hanoun and destroying the al-Amin Muhammad Mosque, various housing blocks, tunnels, homes of Hamas officials (killing the family of Qassam Brigades leader Mohammed Deif), and the Watan Tower (a hub for internet providers in the area). While the IDF placed the West Bank on lockdown, Israel initiated a blockade of the Gaza Strip on 9 October, cutting off its food and fuel supplies, and warning other countries and humanitarian organizations against providing Hamas with the means to fight (by supplying Gaza with essential resources). Hamas responded by threatening to execute its 200 hostages if Israel continued striking homes in Gaza without warning; in response, Israel demanded that residents of Gaza evacuate their homes to save their own lives.
By 13 October 2023, up to 350,000 IDF soldiers had assembled on the border with Gaza. The IDF issued evacuation warnings for communities north of the Wadi Gaza, warning civilians to evacuate Gaza City within 24 hours; this entailed the evacuation of 1.1 million Palestinians, and the UN warned of "devastating humanitarian consequences" before evacuating its facilities to Rafah. Hamas demanded that residents remain in their homes and "to stand firm in the face of this disgusting psychological war waged by the occupation," repeating their practice of using their own civilians as human shields. United States Secretary of State Antony Blinken advised Israel to take care with how it executed the operation, while reassuring Israel of the United States' full support.
On the evening of 13 October, IDF ground troops and armored vehicles entered the Gaza Strip to conduct local raids and rescue hostages from Hamas. Israeli officials claimed that the operation was not part of a larger ground invasion, but rather a raid in which troops only temporarily entered the Gaza Strip. Over the next two days, as Palestinian refugees swarmed into southern Gaza, hundreds were killed by Hamas roadside bombs meant to deter people from leaving the city, while the small town of Khan Yunis became overcrowded with over 1 million refugees and Egypt refused to allow Palestinians to cross its Sinai border, lest it risk young Palestinian males posing a national security threat - Egypt had a troublesome past with both the Muslim Brotherhood (of which Hamas was a splintergroup) and with a Sinai insurgency.
Over the next several days, the violence intensified. On 16 October, Israel ordered 21 Gazan hospitals to evacuate while evacuating 28 of their own communities on the Lebanese border as Hezbollah stepped up its cross-border incursions. The WHO announced that there were only 24 hours of water, electricity, and fuel remaining in the city, while the UNRWA announced that it could no longer deliver assistance to the hundreds of thousands of people in need in Gaza (while 14 UNRWA personnel were killed in Israeli airstrikes on their schools), Hamas terrorists stole fuel and medicine from UN offices in Gaza, Israeli airstrikes on emergency workers and refugee camps resulted in Hamas rocket attacks on Tel Aviv and Jerusalem, Hamas leader Osama Mazini was killed, Israel arrested around 600 people in raids on the West Bank, US Secretary of State Antony Blinken reaffirmed American support for Israel, 49 anti-war protesters were arrested outside the White House while calling President Joe Biden to press for a ceasefire, and hundreds of Americans were evacuated from Haifa to Cyprus aboard cruise ships. On 17 October, 471 Palestinian civilians and 314 others were injured in the Al-Ahli Arab Hospital explosion, which Hamas blamed on Israel, but which was revealed to have been the result of a failed PIJ rocket launch. Palestinian President Mahmoud Abbas declared three days of mourning in Palestine and called off a meeting with Biden, while, that same day, Israel struck a UNRWA school in Gaza, killing 6 people. The Israeli Ministry of Health said that 4,399 people in Israel had been injured since the start of the war, while the WHO reported that 2,800 people had died and 11,000 had been injured in Gaza (half of them women and children), and that Israel had attacked 51 healthcare facilities in Gaza and killed 15 health workers and injured 27 others. Hezbollah, which lost five more fighters in yet another cross-border attack that day, called for a "Day of Rage" on 18 October to coincide with President Biden's visit to the Middle East.
Over the next several days, the IDF promised intensified airstrikes on Gaza, but the United States pressured Israel to delay its ground offensive in order to ensure that hostage negotiations could continue. Hamas began to release a slow trickle of hostages, perhaps in a bid to buy time; two American citizens were released on the Gaza-Israel border on 20 October. The next day, the Rafah border crossing between Egypt and Gaza was finally opened, allowing 20 aid trucks carrying medicine, medical equipment, and flood to enter Gaza. The crossing was closed as soon as the convoy passed through, and its approach to the city was hampered by holes on the main road left by Israeli airstrikes. On 23 October 2023, Israeli defense minister Yoav Gallant said that Israel was preparing for a "multilateral operation" on Hamas from the "air, ground, and sea," while he and Israeli Navy Vice Admiral David Saar Salama toured the Ashdod naval base to assess the Navy's readiness for an operation. By 24 October, the World Health Organization said that nearly two-thirds of hospitals in Gaza were non-functional, while the UNRWA said that the number of aid trucks into Gaza was "a trickle in the face of the immense needs of people." UN Secretary-General Antonio Guterres called for an immediate humanitarian ceasefire in Gaza, saying that there were clear violations of international humanitarian law in the operation, while Human Rights Watch criticized Israel for "deliberately deepening the suffering of civilians in Gaza."
On 25 October, Israel agreed to a request from the United States to get its air defenses in place to protect US troops in the region ahead of an expected ground incursion into Gaza. This occurred as Israel repelled a naval incursion by Hamas militants just north of Gaza, as the leaders of Hezbollah, Hamas, and PIJ met, as the Gaza death toll reportedly reached 6,500, and as the UNRWA warned that it would be forced to shut down within 24 hours if fuel was not delivered to Gaza's hospitals.
On 27 October 2023, the United States announced that Qatari-mediated hostage negotiations had made great progress, and that Hamas expressed a willingness to release all foreign nationals in its custody in exchange for a five-day ceasefire, as well as a willingness to release all hostages if Israel released all female and teenaged prisoners from its custody and if Egypt opened the Rafah border crossing to humanitarian aid. However, that same day saw Israeli admiral Daniel Hagari decry the hostage negotiations as "rumors", and, even as the United Nations debated issuing a resolution calling for an immediate ceasefire (and as the USA called for a humanitarian pause to allow for the evacuation of civilians and the arrival of aid to Gazan civilians), Israel expanded its ground operations. IDF troops operated forcefully on all fronts, launching airstrikes to destroy Gaza's telecommunications service; the Palestine Red Crescent Society lost all contact with its operations room and teams in Gaza, while other Gazan hospitals were disconnected from the outside world. The United States expressed its determination to continue hostage negotiations even as Israel escalated the conflict by invading Gaza.
On 29 October 2023, as the IDF captured as-Siafa and pushed on Beit Hanoun, Iranian president Ebrahim Raisi warned Israel that it had crossed a "red line" with its action in Gaza. At the same time, Netanyahu quoted a Biblical verse about the Amalekites, one of the Israelites' worst enemies, in a speech apparently hinting at genocidal intent. Hamas retaliated against the Israeli invaders with attempted attacks on Erez and Zikim, both of which were repelled.