According to the 16th-century explorer Leo Africanus, the Adal Sultanate's realm encompassed the geographical area between the Bab el Mandeb and Cape Guardafui. It was thus flanked to the south by the Ajuran Empire (Kingdom of Ajuuran) and to the west by the Abyssinian Empire (Abassin Empire).
Adal is mentioned by name for the first time in the 14th century, in the context of the battles between the Muslims of the northern Somali and Afar seaboard and the Abyssinian King Amda Seyon I's Christian troops. Adal originally had its capital in the port city of Zeila, situated in the northwestern Awdal region. The polity at the time was an Emirate in the larger Ifat Sultanate ruled by the Walashma dynasty.
After 1468, a new breed of rulers emerged on the Adal political scene. The dissidents opposed Walashma rule owing to a treaty that Sultan Muhammad ibn Badlay had signed with Emperor Baeda Maryam of Ethiopia, wherein Badlay agreed to submit yearly tribute. This was done to achieve peace in the region, though tribute was never sent. Adal's Emirs, who administered the provinces, interpreted the agreement as a betrayal of their independence and a retreat from the polity's longstanding policy of resistance to Abyssinian incursions. The main leader of this opposition was the Emir of Zeila, the Sultanate's richest province. As such, he was expected to pay the highest share of the annual tribute to be given to the Abyssinian Emperor. Emir Laday Usman subsequently marched to Dakkar and seized power in 1471. However, Usman did not dismiss the Sultan from office, but instead gave him a ceremonial position while retaining the real power for himself. Adal now came under the leadership of a powerful Emir who governed from the palace of a nominal Sultan.
In the 16th century, Adal organised an effective army led by Imam Ahmad ibn Ibrahim al-Ghazi that invaded the Abyssinian empire. This campaign is historically known as the Conquest of Abyssinia or Futuh al Habash. During the war, Ahmed pioneered the use of cannons supplied by the Ottoman Empire, which were deployed against Solomonic forces and their Portuguese allies led by Cristovao da Gama. Some scholars argue that this conflict proved, through their use on both sides, the value of firearms such as the matchlock musket, cannons and the arquebus over traditional weapons. After the death of Imam Ahmad, the Adal Sultanate lost most of its territory in Abyssnian lands. In 1550 Nur ibn Mujahid assumed power after he killed Abyssinian emperor Gelawdewos. Due to constant Oromo raids both Adal and Abyssinian rulers struggled to consolidate power outside of their realms. During the rule of Muhammed Jasa in 1577 he transferred the capital from Harar to Aussa. The Adal Sultanate subsequently ended due to infighting with Somali tribes.
During its existence, Adal had relations and engaged in trade with other polities in Northeast Africa, the Near East, Europe and South Asia. Many of the historic cities in the Horn of Africa such as Abasa and Berbera flourished under its reign with courtyard houses, mosques, shrines, walled enclosures and cisterns. Adal attained its peak in the 14th century, trading in slaves, ivory and other commodities with Abyssinia and kingdoms in Arabia through its chief port of Zeila. The cities of the empire imported intricately colored glass bracelets and Chinese celadon for palace and home decoration.