The Alwaziri coup, also referred as the Yahia clan coup was a violent dynasty overthrow attempt in the Mutawakkilite Kingdom of Yemen in 1948, which created a great deal of violence and ended with around 5,000 fatalities. During the coup attempt, Imam Yahya Muhammad Hamid ed-Din, the ruler of the kingdom, was killed and the rival Sayyid family, the Alwazirs, seized power for several weeks. Backed by the al-Saud family of Saudi Arabia, the Hamidaddins restored their rule. After deposition of the Alwaziris, the restored monarchy of Imam Yahia was succeeded by his son Ahmad bin Yahya.
On 30 October 1918, following the collapse of the Ottoman Empire, Imam Yahya Muhammad Hamid ad-Din of the al-Qasimi dynasty declared northern Yemen an independent state. In 1926, Imam Yahya declared himself king of the Mutawakkilite Kingdom of Yemen, becoming a temporal as well as a (Zaydi) spiritual leader, and won international recognition for the state.
In the 1920s, Yahya had expanded Yemeni power to the north into southern Tihamah and southern 'Asir but collided with the rising influence of the Saudi king of Nejd and Hejaz, Abdul Aziz ibn Sa'ud. In the early 1930s, Saudi forces retook much of these gains in the Saudi-Yemeni War, before withdrawing from some of the area, including the southern Tihamah city of Al Hudaydah. The present-day boundary with Saudi Arabia was established by the 20 May 1934 Treaty of Taif, following the Saudi-Yemeni War of 1934. Yahya's non-recognition of his kingdom's southern boundary with the British Aden Protectorate (later the People's Democratic Republic of Yemen) that had been negotiated by his Ottoman predecessors resulted in occasional clashes with the British.
The Alwazirs (Bayt al-Wazir, of Wadi Sir in Bani Hushaysh), sought to seize power from the ruling dynasty. Imam Yahya was shot by an assassin on 17 February 1948. The assassin, known as Al-Qardaei, was from the Bani Murad tribe. The Alwaziris then installed their own Imam Abdullah bin Ahmad al-Wazir to run the kingdom - which lasted for several weeks.
Upon the murder of Imam Yahya, his son Ahmad bin Yahya traveled through North Yemen, in an attempt to rally the tribes behind him, winning support as the new Imam of Yemen. The supporting tribesmen of Ahmad Hamid al-Din bin Yahia then surrounded Sana'a. As a result, Ahmad was able to regain control of Sana'a, but the price paid was giving the tribes leave to sack the capital. The power was then forcefully reinstalled and the Alwaziri ruler Abdullah deposed and beheaded, in favor of Hamidaddins.
Killed Hamidaddin ruler Imam Yahia was succeeded by his son Ahmad bin Yahya, while the Alwaziris were deposed. Ahmad's reign was marked by growing development, openness and renewed friction with the United Kingdom over the British presence in the south that stood in the way of his aspirations for the creation of Greater Yemen. In March 1955, a coup by a group of officers and two of Ahmad's brothers briefly deposed the king but was quickly suppressed.
After Ahmad's death in 1962, the Crown Prince Muhammad al-Badr was declared king. However, the Kingdom's Hamidaddin dynasty was overthrown the same year escalating into a long civil war between the deposed royalists, supported by Saudi Arabia, and the free officers who declared the YAR, and were actively supported by Nasserist Egypt.