The Raj of Sarawak, Kingdom of Sarawak, or State of Sarawak, was a kingdom founded in 1841 in northwestern Borneo and was in a treaty of protection with the United Kingdom from 1888. It was formed from a series of land concessions acquired by the Englishman James Brooke from the Sultan of Brunei. Sarawak was recognised as a sovereign state by the United States in 1850, and by the United Kingdom in 1864.

Following recognition, Brooke expanded the Raj's territory at the expense of Brunei. Several major rebellions occurred against his rule, causing him to be plagued by debt incurred in countering the rebellions, and the sluggish economic situation at the time. His nephew, Charles Brooke, succeeded James and normalised the situation by improving the economy, reducing government debt and establishing public infrastructure. In 1888, the Raj acquired protected state status from the British Government whilst avoiding cession.

To promote economic growth, Charles Brooke encouraged the migration of Chinese workers from Qing China and British Singapore for agricultural work. With proper economic planning and stability, Sarawak prospered and emerged as one of the world's major producers of black pepper, in addition to oil and the introduction of rubber plantations. He was succeeded by his son, Charles Vyner Brooke, but World War II and the arrival of Imperial Japanese forces ultimately brought an end to the Raj, with the territory placed under British Military Administration upon the Japanese capitulation in 1945, and annexed by Britain as its last acquisition as a Crown Colony in 1946, contrary to the Atlantic Charter.

The Raj was founded by James Brooke, an English former soldier and adventurer who arrived at the banks of the Sarawak River and berthed his schooner there in 1839. After having served in the First Anglo-Burmese War, where he was severely wounded in battle, Brooke returned to England in 1825 to recover from his injury. Despite his attempts to return to service, he was unable to return to his station in India before his temporary leave from the service expired. Overstaying his furlough resulted in his position in the military being forfeited, but he was awarded a pension by the government for his service. He continued on from India and went to China to improve his health.

On his way to China in 1830, he saw the islands of the Asiatic Archipelago, still generally unknown to Europeans. He returned to England and made an abortive trading journey to China in the brig Findlay before his father died in 1835. Inspired by the adventure stories regarding the success of the East India Company (EIC) where his father had been serving, and especially by the efforts of Stamford Raffles to expand the company influence in the Asiatic Archipelago, he purchased a schooner named Royalist using the £30,000 left to him by his father. He recruited a crew for the schooner, training in the Mediterranean Sea in late 1836, before beginning their sail to the Far East on 27 October 1838. By July 1839, he reached Singapore and came across some British sailors who had been shipwrecked and helped by Pengiran Raja Muda Hashim, the uncle of Sultan Omar Ali Saifuddin II of Brunei.

Brooke originally planned to sail to Marudu Bay in northwestern Borneo, but the British Governor-General in Singapore asked him to thank Raja Muda Hashim in southwestern Borneo. He sailed to the western coast of the island the following month, and on 14 August 1839 berthed his schooner on the banks of the Sarawak River and met Hashim to deliver the message. The Raja told Brooke that his presence in the area was to control a rebellion against the Sultanate of Brunei caused by the oppressive policies of Pengiran Indera Mahkota, a kinsman of the Sultan. Mahkota had earlier been dispatched by the Sultan to monopolise the antimony in the area; which as a result directly affected the income of the local Malays there amid growing frustration from the indigenous Land Dayak, who had been forced to work in the mines for about 10 years. It has also been alleged that the rebellion against Brunei was aided by the neighbouring Sultanate of Sambas and the government of the Dutch East Indies, who wanted to establish economic rights over the antimony. Due to these disturbances Brooke had limited access to explore the country, but he managed to explore up the Samarrahan River and spent some time at Rumah Jugah's longhouse at Lundu. On 2 October 1839 he returned to Singapore. Brooke then spent another six months cruising along the coasts of the Celebes Islands before returning to Sarawak on 29 August 1840.

When he returned to Sarawak, the rebellion against Brunei's rule was still ongoing and Hashim asked Brooke to help. Brooke joined Mahkota's forces at Leda Tanah on 18 October 1840. By 20 December 1840 the rebels offered to surrender to Brooke provided they should not be put to death. Hashim initially refused to pardon them and wanted to execute them all, but was convinced by Brooke to forgive them, as Brooke had taken the major part in their suppression. "Hassim agreed to spare the insurgents’ lives and took the wives and children of the insurgency's leaders as hostages. Of the leaders themselves, Datu Patinggi Abdul Gapur and Datu Tumanggong Mersal withdrew to the protection of Sambas, while Datu Patinggi Ali found refuge among the Malays at Sarikei."

In exchange for Brooke's support, Muda Hashim had promised Brooke the country of Siniawan and Sarawak, and its government and trade. On 14 February 1841, Brooke received papers declaring him "resident at Sarawak," which granted him the permission to live in the province, and "to seek profit by trade". Brooke left the next day in the Royalist for Singapore, only to return to Sarawak in May 1841 with a second boat: the Swift, filled with British manufactured goods to trade with Muda Hashim. Brooke was disappointed upon his return that the house Hashim had promised to build for him was not ready, and the antimony he wanted in trade for the manufactured goods had not yet been worked. Furthermore, Hashim began questioning giving the territory to Brooke, which was fanned by Mahkota, who had been deprived of his power in the area in favour of Brooke. This led Hashim to constantly delay the recognition of concession which frustrated Brooke. "Brooke’s estrangement from Hassim provided the Sarawak Malay datus with opportunities to re-establish their positions. They sent a delegation to Brooke led by Datu Tumanggong Mersal and Datu Patinggi Ali’s son, "to request him to become their Rajah, offering to support him by force of arms." On 23 September 1841, Brooke, with the Royalist fully armed, went ashore to Hashim's audience chamber and called on him to negotiate. With little choice, and putting the blame mainly on Mahkota, Hashim granted Sarawak to Brooke on 24 September 1841. Brooke issued new laws for the territory banning slavery, headhunting and piracy; and by July 1842, his appointment was confirmed by Sultan Omar Ali Saifuddin II.