Excerpts from Books and Wikipedia
"A decade after Vasco da Gama's successful voyage around the Cape of Good Hope and to India in 1497–98, the Portuguese arrived in Oman and occupied Muscat for a 143-year period, from 1507 to 1650. Their fortress still remains. In need of an outpost to protect their sea lanes, the Portuguese built up and fortified the city, where remnants of their colonial architectural style still exist. An Ottoman fleet captured Muscat in 1552, during the fight for control of the Persian Gulf and the Indian Ocean. The Ottoman Turks captured Muscat from the Portuguese again between 1581–88. Rebellious tribes eventually drove out the Portuguese, but were themselves pushed out about a century later, in 1741, by the leader of an Omani tribe, who began the current line of ruling sultans. Except for a brief Persian invasion in the late 1740s, Oman has been self-governing ever since." [Wikipedia] "All are known for their oil reserves, from which they earn a consequential foreign income. On a GDP per capita basis, these five are all high-income countries; they are also highly urbanized and quite modern in certain ways but traditional in others; and all are monarchies in the (Sunni) Islamic tradition."