Archaeological evidence suggests that Kedah is the site of Peninsular Malaysia's oldest civilization. Before the sea route around the peninsula was firmly established, trade between India and China was conducted across the peninsular isthmus. One of the primary trading centers for this overland trade was a Hindu-Buddhist kingdom that flourished from the fourth to the seventh century in the Bujang Valley, just south of the peak of Gunung Jerai (and thus easily located by early Indian mariners). Like Malacca a thousand years later, the Bujang Valley civilization attracted a cosmopolitan population of merchants and traders, including Indians, Chinese, Achenese (from Sumatra), Burmese, and Arabs. With the arrival of Arab traders, Islam arrived on the Peninsula for the first time, though the most substantial cultural influence came from Pallava India. As was the case with many of Malaysia's greatest trading civilizations, the Bujang Valley kingdom's prosperity made it an attractive target for outsiders. The region came under the influence of the Sumatran kingdom of Sri Vijaya in the 7th and 8th century, followed by a period during which Kedah was dominated by the Thai states to the north. Kedah's ancient civilization waned in importance by the 15th century, when Malacca assumed a more dominant role. The establishment of Islam in Kedah is due to Malacca's influence.
When Malacca fell to the Portuguese, the influence of its Sultanate over Kedah weakened. However, other powers soon asserted themselves in Kedah, including both the Portuguese and the rising Achenese, and by the end of the 18th century the Thai threat arose once more. Fearing renewed domination by its northern neighbours, Kedah appealed to the British for assistance. As inducements to a commitment, Kedah ceded first Penang (1796) and then the adjoining strip of coastal land (1800) to the British. Nonetheless, Kedah fell to the Thais in 1821. Thailand transferred their sovereignty to the British in 1909. With the exception of the period of occupation by the Japanese during World War II, Kedah remained under British influence until independence.
