Persian Gulf flooding of the basin started 15,000 years ago due to rising sea levels of the Holocene glacial retreat. This inland sea of some is connected to the Gulf of Oman in the east by the Strait of Hormuz; and its western end is marked by the major river delta of the Shatt al-Arab, which carries the waters of the Euphrates and the Tigris. In Iran this is called "Arvand Rood", where "Rood" means "river". Its length is , with Iran covering most of the northern coast and Saudi Arabia most of the southern coast. The Persian Gulf is about wide
Arab states of the Persian Gulf and Oman come in second and third respectively within the regional ranks. The six Arab states of the Persian Gulf lie in a volatile region and their six governments, with varying degrees of success and effort, try and advance peace in their own countries and other countries. However, Arab countries in the Persian Gulf region - specifically Saudi Arabia and Qatar - stand accused of funding Islamist militants such as Hamas and the Muslim Brotherhood. According to the Institute of Economics and Peace (IEP)'s Global Peace Index of 2016, the six governments had varying degrees of success in maintaining peace