The Mutawakkilite Kingdom was an Islamic imamate ruled by the Zaidi Shia Hamid al-Din dynasty. Imam Yahya consolidated power; his son Imam Ahmad continued the rule after his assassination in 1948; Ahmad in turn was succeeded briefly by his son Muhammad al-Badr. Al-Badr had barely been crowned when, on September 27, 1962, army officers inspired by the Arab nationalism of Egyptian President Gamal Abdel Nasser deposed him in a coup, took Sanaa, and proclaimed the Yemen Arab Republic. The overthrow was not clean. Al-Badr survived and fled to the mountains, where Zaidi tribes loyal to the imamate rallied around him. Saudi Arabia and Jordan backed the royalists. Egypt sent tens of thousands of troops to back the republicans. The North Yemen Civil War that followed pitted the two sides against each other in a brutal proxy conflict that dragged on until 1967, when Egyptian troops were withdrawn to fight the Six-Day War. A failed royalist siege of Sanaa in 1968 led most leaders to reconciliation. Saudi Arabia recognized the Republic in 1970.

North Yemen was formally a republic, governed nominally under a constitution adopted in 1970, suspended in 1974, and largely restored between 1978 and the late 1980s. In practice, policy making stayed in the hands of a relatively progressive military elite working with a growing civilian class of technocrats, major tribal leaders, and traditional conservative notables. A succession of bodies performed some legislative functions but exercised little real power until the late 1980s. Political parties were formally banned, though several existed and operated with varying influence during and between elections. It was not a full dictatorship and not a full parliamentary democracy. It was something Yemeni, something improvised, something balanced between tribal authority, military command, and the necessities of running a state in one of the poorest countries in the region.

Unlike East and West Germany or North and South Korea, the Yemen Arab Republic and its southern neighbor the People's Democratic Republic of Yemen - the Marxist-Leninist South Yemen, formed from the former British Aden Protectorate in 1967 - remained relatively cordial. Relations were often strained. Following the Yemenite War of 1972, the two nations declared that unification would eventually occur. These plans were shelved during the Yemenite War of 1979, which was stopped only by Arab League intervention. The goal of unity was reaffirmed at a Kuwait summit in March 1979. North Yemen was overwhelmingly Zaidi Shia and tribal; South Yemen was a secular socialist state with different institutional traditions. That they agreed on unification at all was more surprising than that it eventually ran into trouble.

North Yemen inherited an unusual administrative tradition. The mikhlaf was an ancient Yemeni term for a district, named after a tribal leader, a place, a famous figure, or a well-known town. The name appears on ancient inscriptions in stone. Historians count different numbers of mikhlafs - around 81, by most accounts - and their borders were never fixed. A mikhlaf might contain many subdistricts or shrink to a handful of villages, and sometimes mikhlafs overlapped. The mikhlaf of Dhi Ra'in, for instance, included the mikhlafs of Al-Awd, Hajar, Upper and Lower Yafa', and Jayshan. The system reflects something about Yemeni political identity: overlapping, negotiated, tribal rather than bureaucratic, and rooted in memory of specific people and places rather than abstract lines on a map. When modernity drew borders, the mikhlaf gradually shrank. By the 20th century what remained of the most prominent ones was just a cluster of villages around Yarim.

The path to unification accelerated in May 1988, when the YAR and PDRY agreed to reduce tensions, establish a joint oil exploration area along their undefined border, demilitarize the boundary, and allow Yemenis to cross on national identity cards. Official unification came on May 22, 1990, with a 30-month implementation process planned to finish in November 1992. The first stamp marked Yemen Republic was issued in October 1990. Both currencies remained valid until June 11, 1996. Then came the civil war of 1994, in which southern leaders attempted to secede and were militarily defeated by the north, delaying the final merger and embedding grievances that still run through Yemeni politics. The Houthis, who eventually took Sanaa in 2014 and triggered the current war, emerged from the Zaidi heartlands that had been North Yemen. The southern separatists fighting today trace their roots to the old South Yemen. North Yemen as a distinct state ended in 1990, but what it was - the particular balance of tribe, army, and religious imamate that governed the highlands - is still the ground on which the present wars are being fought.