Asantehene (King of the Ashanti) Kofi Karikari attempted to preserve his empire's last trade outlet to the sea at the old coastal fort of Elmina, which had come into British possession sometime between 1869 and 1872. In early 1873, an Ashanti (Asante) army, a force of somewhere between 12,000 and 60,000 warriors, crossed the Prah (Pra) River. After attacking the Fante, a tribe under British protection, they headed for the coast. The Royal Navy was called in and sent some marines and sailors to man the old slave forts. Elmina was held against a furious Ashanti assault. A river reconnaissance up the Prah was ambushed at Chamah and forced to retreat. A number of landings and naval bombardments were able to slow the Ashanti but not stop them. London realized that an army would have to be sent out to deal with the situation.
The British government then appointed Major General Garnet Wolseley administrator and commander in chief and ordered him to drive the Ashanti from the coastal region. In December 1873, Wolseley's African levies were reinforced by the arrival of several British units, including troops from the Black Watch, the Rifle Brigade, the Welsh Fusiliers, the 2nd West Indies, as well as marines and sailors.
Approximately one month later, Wolseley sent an advance party across the Prah, warning the asantehene that he intended to begin hostilities. Wolseley, however, also offered an armistice. When negotiations failed, both sides prepared for war. The British assembled an expeditionary force numbering about 4000 men, including two units comprised of coastal tribesmen. They headed for the Ashanti capital Kumasi.
The most significant battle of the Second Ashanti War occurred at Amoafo, near the village of Bekwai. Although the Ashanti performed admirably, superior weapons allowed the British to carry the day. Ashanti losses were unknown; the British lost four men and had 194 wounded. In the following days, Wolseley captured Bekwai and then, after another battle outside of Ordahsu, the British entered the Ashanti capital of Kumasi, where there was evidence of human sacrifice, and burnt it. Though Wolseley managed to occupy the Ashanti capital for only one day, the Ashanti were shocked to realize the inferiority of their military and communications systems.
On March 14, 1874, the two sides signed the Treaty of Fomena, which required the Ashanti to pay an indemnity of 50,000 ounces of gold, to renounce claims to Elmina and to all payments from the British for the use of forts, and to terminate their alliances with several other states, including Denkyera and Akyem. Additionally, the asantehene agreed to withdraw his troops from the coast, to keep the trade routes open, and to halt the practice of human sacrifice.
The British victory and the Treaty of Fomena ended the Ashanti dream of bringing the coastal states under their power. The northern states of Brong, Gonja, and Dagomba also took advantage of the Ashanti defeat by asserting their independence. The Ashanti empire was near collapse. By defeating the Ashanti the British had unwittingly destabilized the whole region.
The asantehene, Kofi Karikari, was then deposed, and Mensa Bonsu (ruled 1874-83) assumed power. He attempted to adapt the agencies of Ashanti government to the changed situation. Although he reorganized the army, appointed some Europeans to senior posts, and increased Ashanti resources, he was prevented from restoring Ashanti imperial power by the British political agents, who supported the northern secessionist chiefs and the opponents of central government in Kumasi.
One estimate of casualties suggests that the Ashanti lost about 2000 killed and the British-led force suffered about 1000 killed.