The increased European presence resulted in large part from widespread Qawasim piracy in the early nineteenth century. The British asked the sultan in Oman, to whom the pirates owed nominal allegiance, to end it. When the sultan proved unable, British ships launched attacks on Qawasim strongholds in the present-day UAE as early as 1809; the navy did not succeed in controlling the situation until 1819. In that year, the British sent a fleet from India that destroyed the pirates' main base at Ras al Khaymah, a Qawasim port at the southern end of the gulf. From Ras al Khaymah, the British fleet destroyed Qawasim ships along both sides of the gulf.

The British had no desire to take over the desolate areas along the gulf; they only wished to secure the area so that it would not pose a threat to shipping to and from their possessions in India. Knowing that the sultan in Oman could not be relied upon to control the pirates, the British decided to leave in power those tribal leaders who had not been conspicuously involved with piracy; they concluded a series of treaties in which those leaders promised to suppress all piracy.

As a result of these truces, the Arab side of the gulf came to be known as the "trucial coast." This area had previously been under the nominal control of the sultan in Oman, although the trucial coast tribes were not part of the Ibadi imamate. The area has also been referred to as "trucial Oman" to distinguish it from the part of Oman under the sultan that was not bound by treaty obligation.

In 1820 the British seemed primarily interested in controlling the Qawasim, whose main centers were Ras al Khaymah, Ajman, and Sharjah, which were all small ports along the southeastern gulf coast. The original treaties, however, also involved Dubayy and Bahrain. Although Dubayy and Bahrain were not pirate centers, they represented entrepôts where pirates could sell captured goods and buy supplies. The inclusion of these ports brought two other extended families, the Bani Yas and the Al Khalifa, into the trucial system.

During the next 100 years, the British signed a series of treaties having wide-ranging provisions with other tribes in the gulf. As a result, by the end of World War I, leaders from Oman to Iraq had essentially yielded control of their foreign relations to Britain. Abu Dhabi entered into arrangements similar to those of Dubayy and Bahrain in 1835, Kuwait in 1899, and Qatar in 1916. The treaty whose terms convey the most representative sense of the relationship between Britain and the gulf states was the Exclusive Agreement of 1882. This text specified that the signatory gulf states (members of the present-day UAE) could not make any international agreements or host any foreign agent without British consent.

Because of these concessions, gulf leaders recognized the need for Britain to protect them from their more powerful neighbors. The main threat came from the Al Saud in central Arabia. Although the Turks had defeated the first Wahhabi empire of the Al Saud around 1820, the family rose again about thirty years later; it threatened not only the Qawasim, who by this time had largely abandoned Wahhabi Islam, but also the Al Khalifa in Bahrain and the Ibadi sultan in Oman. In the early 1900s, the Al Saud also threatened Qatar despite its Wahhabi rulers. Only with British assistance could the Al Thani and other area rulers retain their authority.

The Al Saud were not the only threat. Despite its treaty agreement with Britain, Bahrain on several occasions has claimed Qatar because of the Al Khalifa involvement on the peninsula. The Omanis and Iranians have also claimed Bahrain because both have held the island at various times. Furthermore, the Ottomans claimed Bahrain occasionally and tried throughout the latter part of the nineteenth century to establish their authority in Kuwait and Qatar.

The British wished to maintain security on the route from Europe to India so that merchants could safely send goods between India and the gulf. Britain also sought to exclude the influence in the area of other powers, such as Turkey and France.

East-West trade through the Persian Gulf dried up in the nineteenth century after the opening of the Suez Canal, which provided a direct route to the Mediterranean Sea. Gulf merchants continued to earn substantial income from the slave trade, but international pressure, mostly from Britain, forced them to abandon this by 1900. Thereafter, the region continued to profit from the gulf pearl beds, but this industry declined in the 1930s as a result of the world depression, which reduced demand, and as a result of the Japanese development of a cheaper way to "breed" pearls, or make cultured pearls.

Oman, which was technically cut off from the gulf after 1820 when it lost the southern portion of the present-day UAE, fared little better during the late nineteenth century. The fifth sultan in the Al Said line, Said ibn Sultan, ruled for almost the entire first half of the nineteenth century, increasing Omani influence and revenue tremendously. The resulting prosperity, however, was short-lived. The Omani fleet could not compete with the more technologically advanced European ships; thus the sultan gradually lost much of the income he had earned from customs duties on the Indian trade. At the same time, the increasing pressure to restrict the slave trade eliminated much of the revenue the Omanis had earned from East Africa.

The final blow to Oman's economic and political viability came after the death of Said ibn Sultan. When the Al Said could not agree on a successor, the British acted. They divided the Al Said holdings and gave Oman proper to one of the claimants to the throne and awarded Omani possessions in East Africa to another. Thus, after 1856, there were two Al Said rulers. The one in Muscat, with a weakened merchant fleet and no East African revenues, was left with little support. Because of the different centers of power, the country became popularly known as Muscat and Oman.

The sultan's financial weakness contributed to his difficulty in maintaining his hold on the interior. The devout Ibadi population of the interior had long resented the more secular orientation of the coastal centers. As the sultan grew weaker, groups in the interior raised revolts against him on several occasions. Only with British help could the sultan remain in control, and his growing dependence on outsiders caused his relations with the Ibadi population to deteriorate. Whereas other gulf rulers used the British to protect them from their more powerful neighbors, the sultan needed the British to protect him from his subjects.

Data as of January 1993