The Persian Gulf lies between two of the major breadbaskets of the ancient world, the Tigris-Euphrates area (Mesopotamia, meaning "between the rivers") in present-day Iraq and the Nile Valley in Egypt. Mesopotamia, a part of the area known as the Fertile Crescent, was important not only for food production but also for connecting East to West.

Rivers provided the water that made agriculture possible. Agriculture, in turn, enabled people to settle in one area and to accumulate a food surplus that allowed them to pursue tasks besides growing food, namely, to create a civilization. They chose leaders, such as kings and priests; they built monuments; they devised systems of morality and religion; and they started to trade.

Mesopotamia became the linchpin of ancient international trade. The fertile soil between the Tigris and the Euphrates produced a arge surplus of food; however, it did not support forests to produce the timber necessary to build permanent structures. The region also lacked the mineral resources to make metals. Accordingly, the early inhabitants of Mesopotamia were forced to go abroad and trade their food for other raw materials. They found copper at Magan, an ancient city that lay somewhere in the contemporary state of Oman and, via Magan, traded with people in the Indus Valley for lumber and other finished goods.

Trade between Mesopotamia and India was facilitated by the small size of the Persian Gulf. Water provided the easiest way to transport goods, and sailors crossed the gulf fairly early, moving out along the coasts of Persia and India until they reached the mouth of the Indus. Merchants and sailors became middlemen who used their position to profit from the movement of goods through the gulf. The people of Magan were both middlemen and suppliers because the city was a source of copper as well as a transit point for Indian trade. Over time, other cities developed that were exclusively entrepôts, or commercial way stations. One of the best known of these cities was Dilmun.

Dilmun probably lay on what is now the island state of Bahrain. Excavations on the island reveal rich burial mounds from the Dilmun period (ca. 4000 to 2000 B.C.). Scholars believe the monuments on the island indicate that residents, in addition to farming, earned money from the East-West trade and that other cities on the gulf coast survived similarly.

The trading cities on the gulf were closely linked to Mesopotamia, reflected in the similarities between the archaeological finds in the two areas. The similar finds suggest that the people of the gulf coast and the people of the Tigris and Euphrates valley developed increasingly complex societies and beliefs.

The people of the gulf coast differed from those of the interior of the Arabian Peninsula. The people in the interior were nomads who had no time to build cities or monuments and no need to develop elaborate social structures. When the desert provided insufficient food for their flocks, the tribes pushed into the date groves or farmlands of the settled towns. Centers on the gulf coast were subject to such nomadic incursions, as were the people of Mesopotamia. As a result, after the second millennium B.C. the gulf began to take on an increasingly Arab character. Some Arab tribes from the interior left their flocks and took over the date groves that ringed the region's oases, while others took up sailing and began to take part in the trade and piracy that were the region's economic mainstays. These nomadic incursions periodically changed the ethnic balance and leadership of the gulf coast.

Meanwhile, trade flourished in the second millennium B.C., as reflected in the wealth of Dilmun. In about 1800 B.C., however, both the quality and the amount of goods that passed through Dilmun declined, and many scholars attribute this to a corresponding decline in the Mesopotamian markets. Concurrently, an alternate trade route arose that linked India to the Mediterranean Sea via the Arabian Sea, then through the Gulf of Aden, thence into the Red Sea where the pharaohs had built a shallow canal that linked the Red Sea to the Nile. This new route gave access not only to Mediterranean ports but also, through the Mediterranean ports, to the West as well.

One of the ways that rulers directed goods toward their own country was to control transit points on the trade routes. Oman was significant to rulers in Mesopotamia because it provided a source of raw materials as well as a transshipment point for goods from the East. Although a valuable prize, Oman's large navy gave it influence over other cities in the gulf. When Mesopotamia was strong, its rulers sought to take over Oman. When Oman was strong, its rulers pushed up through the gulf and into Mesopotamia. One of the basic conflicts in gulf history has been the struggle of indigenous peoples against outside powers who sought to control the gulf because of its strategic importance.

Competition between Red Sea and Persian Gulf trade routes was complicated by the rise of new land routes around 1000 B.C. Technological advances in the second and first millennia B.C. made land routes increasingly viable for moving goods. The domestication of the camel and the development of a saddle enabling the animal to carry large loads allowed merchants to send goods across Arabia as well. As a result, inland centers developed at the end of the first millennium B.C. to service the increasing caravan traffic. These overland trade routes helped to Arabize the gulf by bringing the nomads of the interior into closer contact with their relatives on the coast.

Data as of January 1993