His work in Sierra Leone, specifically in Freetown, shaped the region, pioneering the expansion of the Church Missionary Society and advancing Western influence and beliefs in that area.
Hartwig studied Susu at the School for Africans under William Greaves, a missionary from Edinburgh who had previously worked in Sierra Leone before returning to the UK.
[1] Hartwig's decision to become a missionary was initially motivated by his desire to avoid serving in the military, as revealed in a letter written by fellow missionary Gustavus Reinhold Nylander: "He did not like to be a soldier in the Prussian army and for fear of being forced to it was custom in Prussia, he joined the mission, only to get out of his native country by that means" (CMS Archives, CA1/E1/110, Nylander to Pratt, Freetown, 10 July 1807).
Freetown was created for formerly enslaved Africans who fought for the British Crown in the American Revolutionary War and were previously in America and Britain.
In addition, he was instructed to maintain frequent contact with the CMS by sending periodical reports as well as keeping a journal describing his experiences.
As Hartwig was learning Susu and Arabic, he was instructed by the CMS to make regular journeys outside the colony to assess the character and customs of the local populations living further inland.
His frequent absence left Renner to shoulder the responsibilities in Freetown alone, confined to what he felt was a place ravaged by sickness and starvation.
Establishing strong ties with the local community was important to the success of a mission, offering missionaries access to scarce medical resources, critical information, travel opportunities, and increased influence and respect.
His wife Sarah suffered from even more frequent bouts of illness, so even when Hartwig was in good health, he had to take time away from the community to care for her.
In their letters to home, fellow missionaries noted his struggles with the language, while the Corresponding Committee in Freetown blamed his accent for his ineffectiveness in reaching the community.
The settlement's population was a mix of diverse groups, including many settlers who had originally left the United States after the 1763 American War of Independence and relocated to Africa.
[5] By 1808, the financial strain of sustaining the colony led to the collapse of the Sierra Leone Company, prompting the British Crown to annex Freetown.
The settlement then became a hub for enforcing the Act to Abolish Slavery, with a Vice Admiralty Court established to adjudicate cases involving captured slave ships.
From this point onwards, the CMS became more structured and played a pivotal role in shaping Christian communities among the freed African population in Sierra Leone.