More than 700 people were killed in Israel after Hamas militants launched a surprise attack on Saturday.
Tel Aviv called it an act of war, and immediately issued a bloody response which left 400 Palestinians dead.
The shocking brutality of this crisis has already stunned the international community – but, it is a conflict which has been ongoing for decades.
Hamas, a Palestinian Islamist group, has been described as terrorists by supporters of Israel who believe this was an unjust attack.
Critics of Tel Aviv claim they are fighters who are liberating the Palestinian territories in an act of revolution against Israeli occupation.
This issue, which dates back to 1948, is incredibly fraught – but this latest development has caused more division than ever.
So, here’s a basic explanation unpacking why it’s so contentious, and who has sided with whom.
What’s happened?
Hamas took the Middle East’s strongest army by surprise on Saturday with its multi-pronged offensive.
At least 2,200 rockets and mortars were launched into Israeli territory on Saturday morning, and bulldozers were used to knock down the physical barriers around parts of occupied Palestinian land.
Hamas militants crossed into 22 Israeli towns and army bases by every means possible for battle, leading to the first conflict on Israeli soil for decades.
A senior official from Knesset (Israel’s parliament) claimed the attack led to the most civilian deaths on a single day in Israel’s history.
Fighters also abducted party-goers from a rave near the kibbutz of Re’im, including at least one Israeli soldier, keeping them hostage in Gaza. At least 260 bodies were later found where the music festival was held, too.
Hamas militants stormed Israeli towns, killing 700 civilians and abducting dozens. Sources told Reuters that the group had been practising attacks for months, having even constructed a mock Israeli settlement where it could rehearse its offensives.
Israel’s army spokesman, Major Nir Dinar, said: “This is our 9/11. They got us.”
He added: “They surprised us and they came fast from many spots – both from the air and the ground and the sea.”
It was the worst breach in Israel’s defences since armies in Egypt and Syria waged the Yom Kippur War in 1973. Tel Aviv only managed to repel the Arab forces at the time because the US got involved, and provided direct support.
For the last two years – following a spate of violence between the two sides in 2021 – Hamas had been suggesting they were not interested in further conflict.
The group said it would prioritise getting economic incentives to Palestinians in Gaza, so they could work in Israel or the West Bank.
Hamas also didn’t join in with another Gaza-based islamist armed group, Islamic Jihad, when it launched attacks against Israel – meaning Saturday’s offensive caught Tel Aviv completely unaware.
Biden’s national security adviser Jake Sullivan said only last week: “The Middle East region is quieter today that it has been in two decades.”
It’s also a notable attack because most battles between Israel and the Arab states have also been fought outside of its borders, or through rocket artillery.
Immediately after the offensive, Israeli PM Benjamin Netanyahu said: “Our enemy will pay a price the type of which it has never known. We are in a war and we will win it.”
Israel has since hit back and killed 400 Palestinians in Gaza, and ordered a complete siege of the area.
Israeli defence minister Yoav Gallant said: “I have ordered a complete siege on the Gaza Strip. There will be no electricity, no food, no fuel, everything is closed. We are fighting human animals and we act accordingly.”
Why has this area been occupied by conflict for so long?
This part of the Middle East has been torn apart with tensions for decades, and there have been many failed attempts to establish peace.
It ultimately comes down to a dispute about who the land belongs to – Israeli Jews or Palestinian Arabs. The region is holy to both populations (as well as Christians).
Both sides suggest they have a claim to the land which stretches back centuries, although tensions only really started to escalate in the early 20th Century.
With Britain’s support, Israel officially became the world’s only Jewish state in 1948 following an influx of Jewish migrants who believed in Zionism – that’s the establishment of a Jewish state in Palestine.
The land was predominantly occupied by Palestinian Arabs up until this point, and widely known as Palestine, so the UN wanted to divide the country so both populations could stay there, while putting the capital Jerusalem under international control.
But once it gained independence, Israel immediately faced pushback from five neighbour Arab states. When this conflict was resolved, Israel had more land and more Jewish occupants from surrounding countries, while more Palestinian Arabs had fled.
A subsequent war in 1967 saw Israel occupy the West Bank and the Gaza Strip. Today, the West Bank is controlled by the Palestinian Authority but under Israeli occupation, while Gaza is controlled by Hamas but under Israeli blockade.
Israel’s extreme-right government has also escalated its strict occupation in the West Bank, as Israeli security forces and settlers upping the violence towards Palestinians.
The main proposal for peace is the idea of a two-state solution, which would establish Gaza and most of the West Bank as the independent state of Palestine.
But with the two sides continuing to fight so violently, it seems increasingly unlikely this would work.
What may have triggered this particular act of aggression?
There does not appear to be one sole reason Hamas launched this attack now.
According to the New York Times, the leader of Hamas’ military wing, Muhammad Deif, said that the group wanted to launch an “operation” so “the enemy will understand that the time of their rampaging without accountability has ended”.
He pointed to Israel’s occupation of the West Bank – dating back to 1967 – and the detention of thousands of Palestinians in Israeli jails as motives for the attacks.
He also referred to the recent tension over the Temple Mount or the Al-Aqsa Mosque (known as the Noble Sanctuary within Judaism), a site in Jerusalem which is holy to both religions.
Palestinian worshippers have been harassed and attacked at the site recently by Israeli police. Meanwhile, even though it goes against Jewish law, Israeli Jews have started to worship there.
Hamas has since named its offensive Operation Al-Aqsa Storm.
Another factor in the sudden escalation of violence may be what the UN describe as the “chronic humanitarian crisis” in Gaza.
It’s been blockaded by Israel ever since Hamas took control of the territory in 2007. Egypt has restrictions on movements in the south, too, and it’s often targeted by Israeli bombardments.
US-based outlet Vox also suggested that US President Joe Biden’s focus on Israel-Saudi talks could have accelerated violent action. Saudi Arabia has never recognised Israel out of loyalty to Palestine, but may have been on the cusp of changing direction.
The US president also did not reverse Donald Trump’s policy of putting Palestine on the back burner, even as Israel’s government lent further right.
In fact, negotiations between Israel and the Palestine Liberation Organisation have been on hold ever since 2014, when Barack Obama was in the White House.
The US has also declared Hamas a terrorist organisation, meaning it cannot work directly with them, only through third countries.
There may have been other forms of symbolism at play with the timing of the attack, too. This weekend marked the 50-year anniversary of the Yom Kippur War, when Israel was taken aback by attacks from Egypt and Syria, and came on the final day of the Jewish celebration of the harvest.
It may have been strategically timed as well. Israel has been facing a difficult domestic period, because of the far-right government’s efforts to reduce the judiciary’s powers.
Who supports who?
The US, the UK and the EU – among others – have openly voiced their support for Tel Aviv and reiterated its right to defend itself against “Hamas terrorists”.
Washington DC has also offered several US Navy warships and aircraft squadrons, while NATO has condemned the “terrorist attacks by Hamas against NATO partner Israel” too.
Ukrainian president Volodymyr Zelenskyy said it was a “terror attack” on Israel and that Israel’s right to defend itself “cannot be doubted”.
The UN’s spokesperson, Stephane Dujarric, said the secretary-general “is deeply concerned for the civilian population and urges maximum restraint”.
Egypt and Jordan have offered to try and defuse the situation through diplomacy, with both countries warning about the volatility of the situation.
Saudi Arabia, which is looking to normalise relations with Israel, called for de-escalation.
Publicly, Russia has called for “restraint”, along with Turkey.
Iran and Hezbollah, the Iran-backed Shia militant group based in southern Lebanon, have praised Hamas’ actions.
Hezbollah said it was “in direct contact with the leadership of the Palestinian resistance”, saying it was a “decisive response to Israel’s continued occupation and a message to those seeking normalisation with Israel.”
Meanwhile, an adviser to the Supreme Leader in Iran said: “We congratulate the Palestinian fighters. We will stand by the Palestinian fighters until the liberation of Palestine and Jerusalem.”
The Arab League has called for the end of “armed confrontation between the two sides”, while lashing out at Israel’s “continued implementation of violent and extremist policies”.
Venezuela appears to have sided with Palestine, saying the fighting was “the result of the impossibility of the Palestinian people to find multilateral international legality a space to assert their historic rights”.
Yemen’s Houthi rebels also supported “the heroic jihadist operation”.