The PFLP sparked the war when it hijacked four jetliners, diverted three of them to a Jordanian air strip, blew them up, and for three weeks held on to dozens of the 421 hostages it seized as human bargaining chips.
Why Palestinians Turned on Jordan
In 1970, some two-thirds of the Jordanian population was Palestinian. After the Arabs' defeat in the 1967 Arab-Israeli War, or Six Day War, Palestinian militants took part in the War of Attrition against Israel. The war was mostly fought in the Sinai between Egyptian and Israeli forces. But the PLO launched raids from Egypt, Jordan and Lebanon as well.
The Jordanian king had not been keen to fight the 1967 war, nor was he eager to keep letting Palestinians attack Israel from his territory, or from the West Bank, which had been under Jordanian control until Israel occupied it in 1967. King Hussein had maintained secret, cordial relations with Israel through the 1950s and 60s. But he had to balance his interests in preserving a peace with Israel against a restless and increasingly radicalized Palestinian population, which was threatening his throne.
Jordanian army and Palestinian militias led by the PLO fought several bloody battles in the summer of 1970, most violently during the week of June 9 to 16, when 1,000 people were killed or wounded. On July 10, Hussein signed an agreement with the PLO's Yasser Arafat pledging support to the Palestinian cause, non-interference in Palestinian commando raids on Israel in exchange for a Palestinian pledge to support Jordanian sovereignty and remove most Palestinian militias from Amman, the Jordanian capital. The agreement proved hollow.
Promise of Hell
When Egypt's Gamal Abdel Nasser agreed to a cease-fire in the war of attrition, and King Hussein supported the move, George Habash, the PFLP leader, promised that "we will turn the Middle East into a hell," while Arafat invoked the battle of Marathon in 490 BC and vowed, before a cheering crowd of 25,000 in Amman on July 31, 1970, that "We will liberate our land."
Three times between June 9 and Sept. 1, Hussein escapes assassination attempts, the third time as would-be assassins open fire on his motorcade while he drove to Amman airport to meet his daughter Alia, who was returning from Cairo.
Between Sept. 6 and Sept. 9, Habash's militants hijacked five planes, blew up one, and diverted three others to a desert strip in Jordan called Dawson field, where they blew up the planes on Sept. 12. Rather than receiving the support of King Hussein, the Palestinian hijackers were surrounded by units of the Jordanian military. Even though Arafat worked for the release of the hostages, he also turned his PLO militants loose on the Jordanian monarchy. A bloodbath ensued.
Up to 15,000 Palestinian militants and civilians were killed, swaths of Palestinian towns and refugee camps, where the PLO had massed weapons, leveled, the PLO leadership decimated, and between 50,000 and 100,000 people were left homeless. Arab regimes criticized Hussein for what they called "overkill."
Before the war, Palestinians had run a state-within-a-state in Jordan headquartered in Amman. Their militias ruled the streets and imposed brutal and arbitrary discipline with impunity.
Hussein ended the Palestinians' reign.
The PLO Is Thrown Out of Jordan
On Sept. 25, 1970, Hussein and the PLO sign a cease-fire mediated by Arab nations. The PLO temporarily maintains control over three towns--Irbid, Ramtha and Jarash, as well as Dawson Field, or Revolution Field, as the PLO termed it, where the hijacked planes had been blown up.
But the PLO's last gasps were short-lived. Arafat and the PLO were expelled from Jordan by early 1971. They went to Lebanon, where they proceeded to create a similar state-within-a-state, weaponizing a dozen Palestinian refugee camps around Beirut and in South Lebanon, and destabilizing the Lebanese government as they had the Jordanian and playing a leading role in two wars---the 1973 war between the Lebanese army and the PLO, and the 1975-1990 civil war, in which the PLO fought alongside leftist Muslim militias against Christian militias.
The PLO was expelled from Lebanon following Israel's 1982 invasion.
Black September's Consequences
Besides seeding Lebanon's civil war and disintegration, the Jordanian-Palestinian war of 1970 led to the creayion of the Palestinian Black September movement, a commando faction that broke away from the PLO and directed several terrorist plots to avenge Palestinians' losses in Jordan, including hijackings, the assassination of the Jordanian prime minister, Wasif al-Tel, in Cairo on Nov. 28, 1971, and, most notoriously, the murder of 11 Israeli athletes at the 1972 Munich Olympics.
Israel, in turn, unleashed its own operation against Black September as Israeli prime Minister Golda Meir ordered the creation of a hit squad that fanned out in Europe and the Middle East and assassinated numerous Palestinian and Arab operatives. Some were connected with Black September. Some were not, including the murder of Ahmed Bouchiki, an innocent Moroccan waiter, in the Norwegian ski resort of Lillehammer in July 1973.