Sultan Said introduced cloves to the island in the early 1800s and, together with the lucrative slave trade that ran out of Zanzibar, put his empire in riches. Things were going so well for the Sultan in Zanzibar that, around 1840, he decided to move the Sultanate capital from Muscat to Unguja.

By mid 19th century, Zanzibar was the world's leading clove exporter as well as a large exporter of slaves. A reported 25,000 slaves passed through Zanzibar every year. Slave trader Tipu Tip got so rich off the trade that he was able to afford over thirty concubines and their children in addition to his official wife and her two children.

After Sultan Said died in 1856 (on a boat while returning to Zanzibar from a placating visit to Oman), the royal family faced a series of near debilitating power struggles. Plagued by jealousy, intrigue, and the abolition of slavery, the sultans and their subjects faced a post-heyday slump during which the British were successful in wresting away from them much of the control of the island.

The British had been trying to abolish the slave trade from the island since Sultan Said's rule but had only been successful in effecting quotas and intimidating traders of certain nationalities. After his death, the British succeeded in pressuring Said's successors to stop the slave trade on Zanzibar.

In 1873, Sultan Barghash signed a treaty agreeing to the end of the slave trade in his dominions but didn’t honor it. By 1890, Sultan Ali, the last of Sultan Said's successors, signed the third treaty of its kind promising an end to the slave trade in Zanzibar. This one stuck and all slaves to enter the area after that date were declared free and no more were sold.

On August 25, 1896, Sultan Hamed bin Thuwain (Grandson of Said the Great) died leaving the Sultanate's throne empty. Hamed's cousin, Khaled (the son of former Sultan Barghash,) claimed the throne by crawling through a window of the ceremonial palace, collecting supporters and then announcing that he was the new Sultan. During this time Zanzibar was a Protectorate under the British Government, and they were not about to release control of the island to an attempted palace coup. On August 26th they sent an ultimatum to Khaled stating that the British would use force if he did not lower his flag by 9:00 a.m. the next day. On August 27th in the early morning hours, the European women were shuttled to a boat offshore to wait out the day. At 9:00 a.m., with Khaled's flag still flying, the British opened fire and in forty minutes managed to destroy the Palace, the Harem, the Sultan's ship, the Glasgow, and the lighthouse, leaving the House of Wonders only slightly damaged. At 9:45am the war was over and Seyyid Hamoud bin Muhammed was proclaimed as the new, and British- approved, Sultan. The war lasted only forty-five minutes and is listed in the Guinness Book of World Records as the shortest war in history.

From 1902 to 1970 Zanzibar was home to at least fifty newspapers, most of which were published in English, Swahili and/or Gujarati, an Indian language.

The British Protectorate continued until, realizing that independence was looming for the islands, the British granted them independence in June of 1963. Constitutional independence was established on December 10th, 1963 and control of the islands was passed to the constitutional monarch. The new monarchy didn't last long, however, because on January 1964, just a month later, a violent revolution resulted in the emergence of the People's Republic of Zanzibar led by President Karume, the leader of the Afro-Shirazi Party. The revolution was brief but brutal; over 17,000 Arabs and Indians were killed in a period of several days. Many of the remaining Asians and Arabs left the island and their possessions and land were nationalized.

On April 24, 1964 Zanzibar joined with Julius (Mwalimu – Swahili for 'teacher') Nyerere's Tanganyika to form modern day Tanzania. Zanzibar's autonomous state included a constitutional right to keep its own President, Chief Minister, Cabinet and House of Representatives. The union did not place Zanzibar at the feet of Tanzania, and Karume managed to keep profits from the clove plantations on Pemba without having to give any over to the mainland.

In the late 1980s Zanzibar opened to the idea of free market and started to take advantage of its tourism potential. Zanzibar held its first multi-party elections in 1995.

1998 marked the year of Zanzibar's first traffic light.