Which Middle Eastern nation was divided into two countries between 1967 and 1990?

Yemen, officially known as the Republic of Yemen, is an Arab country in Western Asia at the southern end of the Arabian Peninsula. Yemen is the second-largest country in the peninsula, occupying 527,970 km2 (203,850 sq mi). The coastline stretches for about 2,000 km (1,200 mi). It is bordered by Saudi Arabia to the north, the Red Sea to the west, the Gulf of Aden and Arabian Sea to the south, and Oman to the east-northeast.

Administration of Yemen has long been notoriously difficult. Several dynasties emerged from the ninth to 16th centuries, the Rasulid dynasty being the strongest and most prosperous. The country was divided between the Ottoman and British empires in the early twentieth century. The Zaydi Mutawakkilite Kingdom of Yemen was established after World War I in North Yemen before the creation of the Yemen Arab Republic in 1962. South Yemen remained a British protectorate known as the Aden Protectorate until 1967 when it became an independent state and later, a Marxist state. The two Yemeni states united to form the modern republic of Yemen in 1990.