The Republic of Yemen, commonly known as Yemen, is a country located in Western Asia, occupying the southwestern to southern end of the Arabian Peninsula. 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. Yemen is considered one of the poorest countries in the Arab world. Its capital and largest city is Sana'a. Yemen's territory includes over 200 islands, the largest of which is Socotra, about 354 km (220 mi) to the south of mainland Yemen. It is the only state in the Arabian Peninsula to have a purely republican form of government. Yemen was the first country in the Arabian peninsula to grant women the right to vote. Yemeni unification took place on 22 May 1990, when North Yemen was united with South Yemen, forming the Republic of Yemen.