Arab migration to Oman started from northern-western and south-western Arabia and those who chose to settle had to compete with the indigenous population for the best arable land.
Imamate of Oman:
The first Imamate reached its peak power in the ninth A.D. century. The Imamate established a maritime empire whose fleet controlled the Gulf during the time when trade with the Abbasid Dynasty, the East and Africa flourished. The authority of the Imams started to decline due to power struggles, the constant interventions of Abbasid and the rise of the Seljuk Empire.
During the 11th and 12th centuries, Oman was controlled by the Seljuk Empire. They were expelled in 1154, when the Nabhani dynasty came to power.
The Nabhanis ruled as muluk, or kings, while the Imams were reduced to largely symbolic significance. The Nabhani dynasty started to deteriorate in 1507 when Portuguese colonizers captured the coastal city of Muscat, and gradually extended their control along the coast.
In need of an outpost to protect their sea lanes, the Portuguese built up and fortified the city, where remnants of their Portuguese architectural style still exist. Later, several more Omani cities were colonized in the early 16th century by the Portuguese, to control the entrances of the Persian Gulf and trade in the region as part of a web of fortresses in the region, from Basra to Hormuz.
During the 17th century, the Omanis were reunited by the Yaruba Imams. Nasir bin Murshid became the first Yaarubah Imam in 1624, when he was elected in Rustak. Imam Nasir succeeded in the 1650s to force the Portuguese colonizers out of Oman. The Omanis over time established a maritime empire that later expelled the Portuguese from East Africa, which became an Omani colony. The rivalry within the house of Yaruba over power after the death of Imam Sultan in 1718 weakened the dynasty. With the power of the Yaruba Dynasty dwindling, Imam Saif bin Sultan II eventually asked for help against his rivals from Nader Shah of Persia. A Persian force arrived in March 1737 to aid Saif. From their base at Julfar, the Persian forces eventually rebelled against the Yaruba in 1743. The Persian empire then colonized Oman for a short period until 1747.
British de facto Colonization:
The British empire was keen to dominate southeast Arabia to stifle the growing power of other European states and to curb the Omani maritime power that grew during the 17th century. The British empire over time, starting from the late 18th century, began to establish a series of treaties with the sultans with the objective of advancing British political and economic interest in Muscat, while granting the sultans military protection. In 1798, the first treaty between the British East India Company and Albusaidi family was signed by Sultan bin Ahmed. The treaty was to block commercial competition of the French and the Dutch as well as obtain a concession to build a British factory at Bandar Abbas. A second treaty was signed in 1800, which stipulated that a British representative shall reside at the port of Muscat and manage all external affairs with other states. The British influence that grew during the nineteenth century over Muscat weakened the Omani Empire.