The British traders regularly advanced goods to Smart to go inland as a slave-buying agent. after they had built up a lot of confidence in him. Instead of always buying slaves for his British owners, he sometimes bought his own Loko people, not to be sold as slaves, but to become his own followers. By this process, he built up a powerful force around the middle Rokel River, and ultimately severed connection with his former British masters at Bunce Island. He had become too powerful for them even to ask him for a refund of the goods they had advanced him. In fact, in 1806, one of the British employees of Bunce Island visited Gurnbu Smart at Rokon and then wrote about him admiringly in a book he published the following year.
To enhance his military skills and build up alliances. Smart joined the Wunde society which spccialises in military training. He then took the name of "Gurnbu" meaning "fire" in Mende. Whcn war erupted between the Ternne of Masimera and Marampa , Gurnbu Smart was called to help Masirncra and, as a reward, was given control of the Town or Rokon, where he settled with his followers. Rokon under Gumbu Smart became a large well-laid-out town with wide streets and well-built houses. It became the most powerful settlement in the area and a major commercial centre. Gurnbu Smart played an important role in regulating the commerce passing down the Rokel River on the way to the Atlantic coast. After the founding of the Freetown colony, he was also engaged in active trading with the new settlement. Gurnbu Smart, an accomplished diplomat was careful to maintain alliances. In the 1790s, he made friends with the officials of the Siena Leone Company which ruled the Freetown settlement. European missionaries of the London Missionary Society were sent to Rok on , and Gurnbu Smart received them warmly. Though the missionaries did no conversion, one of them. Henderson wanted to marry Gumbu Smart's young daughter. Smart even helped the Sierra Leone Company in its wars against the Koya Tcmne , led by King Tom in 1801.
Gumbu Smart died about the IX20s and he left behind a rich legacy of dynamism and enterprise. Indeed. it is not surprising that the Smart family. descended from Gumbu, has given Sierra Leone so many outstanding leaders down through the years.