Prior to the end of World War I, North Yemen was vilayet of the Ottoman Empire. Following the collapse of the Ottoman Empire in 1918, Immam Yahya Muhammad of the al-Qasimi dynasty declared northern Yemen independent. North Yemen continued to be a kingdom until 1962 when a civil war broke out between republicans and royalists. The war ending in 1970 with the Yemen Arab Republic being established.
The North and South Yemen remained divided until they reunited in May of 1990. Yemen remained united until the former South Yemeni governorates united and declared themselves independent again as the Democratic Republic of Yemen, resulting in a three month civil war that ended with the south regaining its independence.
North Yemen became part of the Arab Spring when revolution broke out in 2011, which ousted Ali Abdullah Saleh from power. After the establishment of a new government, North Yemen officially recognized the sovereignty of South Yemen (though border refugees continue to be a problem between the two countries).