Yemen, Republic of, nation in south-western Asia, on the south-western coast of the Arabian Peninsula, formed in 1990 through the union of the People's Democratic Republic of Yemen and the Yemen Arab Republic. Yemen is bordered on the north by Saudi Arabia, on the east by Oman, on the south by the Gulf of Aden, and on the west by the Red Sea. The interior boundaries are mostly undemarcated. Yemen includes the islands of Socotra in the Gulf of Aden, Kamaran in the Red Sea, and Perim in the strait of Bab el Mandeb. The area of Yemen is about 536,869 sq km (207,285 sq mi). The capital of the Republic of Yemen is Sana'a.