Arabia is mainly a great plateau of ancient crystalline rock, largely covered with limestone and sandstone. It rises steeply from the narrow Red Sea coastal plain, achieving its greatest height (c.12,000 ft/3,700 m) in SW Arabia, and slopes gently E to the Persian Gulf; the Oman Mts., SE Arabia, rise to c.10,000 ft (3,000 m). The coastal mountains catch what little moisture is carried by the dry winds that cross Arabia, making the interior so arid (4 in./10 cm annual precipitation) that there is not a single perennial stream; thus, large areas lack water. The basin-shaped interior consists of alternating steppe and desert landscape; the Nafud desert in the north is connected with the great Rub al-Khali in the south (one of the world's largest sand deserts) by the Dahna, a narrow sand corridor.

Extensive and varied agriculture (coffee, grains, fruits) exists only in SW Arabia, particularly in Yemen, where high coastal mountains intercept the moist southwest monsoon winds during the summer. The northeast coast of Oman has a climate similar to that of Yemen, but in most of Arabia rainfall occurs only in winter. The coastal lands, however, are much more humid than the interior; fog and dew are common. Desalination plants supply much of the population's drinking needs. Osmosis distillation processes take brackish underground water and make it useful for agriculture and industry.

The majority of the Arabian population is sedentary, concentrated around oases, notably in the Nejd (central Arabia) and the Hejaz (along the northeast coast of the Red Sea). Agriculture is the main occupation, with dates, grains, and fruits the chief crops; pastoral nomads raise goats, cattle, sheep, and poultry. Until the mid-20th cent., when oil was discovered in E Arabia, the peninsula's main exports were hides, wool, coffee, spices, camels, and the famed, highly bred Arabian horses; in W Arabia pearls were exported. With the exception of Aden, Arabia did not have a good port until after World War II, when modern port facilities were constructed, especially along the Persian Gulf. Arabia has the largest oil reserves in the world, in addition to great amounts of natural gas. Saudi Arabia is the world's leading exporter of oil. Until the early 1970s, oil firms from the United States, Britain, and to a lesser extent Japan, had a monopoly on drilling concessions. However, the Arabian nations acquired much greater control over oil exploration, production, and price controls after 1970. Modern technology and the huge wealth generated by oil resources have profoundly altered traditional life in Arabia. Flourishing private enterprise, new transportation links, rapidly growing cities, a large foreign labor presence, and rising education and living standards characterize much of the peninsula.

Archaeological evidence points to ancient trade ties between Yemen and the NE African coast. However, little is definitely known of Arabian history in the period preceding the oldest inscriptions discovered—those dating from c.1000 b.c. In those times much of SW Arabia was divided among the domains of Ma'in, Sheba, and Himyar. Political unity in Sheba seems to have been hastened by Darius's conquest of N Arabia.

No ancient power ever attempted the complete conquest of Arabia because of the formidable obstacles of crossing the deserts. Rome invaded (24 b.c.) N Arabia but soon withdrew, although for a long period it held N Hejaz. Ethiopia, during its great expansion under the Aksumite kings (see Aksum), twice (a.d. 300-378 and 525-70) held Yemen and the Hadhramaut. In 570 the Sassanids of Persia drove out the Ethiopians and established a short-lived hegemony over the peninsula.

Arabia was briefly unified after the founding of Islam by Muhammad, the prophet of Mecca, in the 7th cent. His dynamic faith, furthered by his successors, reconciled the warring Arab tribes and soon sent them out on a career of conquest. They overran N Africa and SW Asia and gained control of Spain and S France until they were stopped in the west by the Frankish ruler Charles Martel in 732 and in the east by the Byzantine Empire c.750. However, the tremendous territorial expansion of Islam diminished its exclusively Arab character, and the need for a more centralized administrative center led to the transfer of the seat of the caliphate from Medina to Damascus. Independent emirates arose in Yemen, Oman, and elsewhere. In the 10th cent. a semblance of unity was imposed by the Karmathians, a Muslim sect, but in the 11th cent. anarchic conditions again prevailed.

After the discovery of the route to India around the Cape of Good Hope in 1498, European powers were attracted to Arabia as a site for trading bases. The Portuguese seized Oman in 1508 but were driven out in 1659 by the Ottoman Empire, which attempted, but never with complete success, to control all Arabia. Great Britain established a physical presence in Arabia in 1799 by occupying Perim Island in the Bab al-Mandeb; and in 1839 the Ottoman Empire lost Aden to the British. In 1853 Britain and the E Arabian sheikhs signed the Perpetual Maritime Truce, by which the Arabs agreed not to harass British shipping in the Arabian Sea and recognized Britain as the dominant foreign power in the Persian Gulf. The truce confirmed the temporary truces of 1820 and 1835; the sheikhdoms were thus called the Trucial States.

Arab nationalist opposition to the Ottoman Turks was aroused in the mid-19th cent. by a rekindling of the Wahhabi, a reform movement within Islam; it waned toward the end of the century. Just before World War I, Ibn Saud revived Wahhabi ideology, and during the war he signed a military pact with Britain against the Turks. His strongest rival, Husayn ibn Ali of the influential Hashemite family, led a successful revolt against the Turks in the Hejaz and set up an independent state there. After the war, however, the Saud family prevailed in a violent struggle against Husayn and other Arab families, and Ibn Saud was proclaimed king of the Hejaz in 1926. In 1932 the Hejaz and outlying areas were incorporated officially into the Kingdom of Saudi Arabia. The Hashemites were rewarded for their war efforts on behalf of the Allies by being installed in Transjordan and Iraq. Between the world wars, Britain was the dominant foreign power in Arabia, holding protectorates over the Arab sheikhdoms. The post-World War II era witnessed a significant decline of Britain's presence, culminating in the withdrawal of British military forces E of Suez in the late 1960s.

Both the United States and the USSR sought to fill the vacuum created by Britain's withdrawal from the oil-rich, strategically important peninsula. By the early 1970s, however, the Arab nations were asserting their independence with growing success, primarily due to the enormous oil revenues brought to many of the Arabian countries. The Arab oil boycott in 1973, marked by international oil price increases (particularly notable in the United States), exemplified growing Arabian economic power. By the mid-1980s, Saudi Arabia had acquired complete control of the Arabian American Oil Company (ARAMCO), which had first discovered oil there in the 1930s and was previously owned by American firms. The economic power of the Arabian countries has continued to grow as oil exports have increased. These countries account for some of the highest per capita incomes in the world. Although they were only peripherally involved in the Arab-Israeli Wars, Arabian oil interests were dangerously threatened as a result of the Iran-Iraq War (1980-88). The area became directly involved militarily and territorially after Iraq invaded Kuwait in Aug., 1990. (see Kuwait and Persian Gulf War).