Why did David Livingstone become a national hero in Britain after returning in 1856?

David Livingstone became a national hero in Britain upon his return in 1856 primarily because news of his arduous, multi-year explorations across Africa had captivated the public imagination to an unprecedented degree.1

His status was cemented by his ambitious vision to open the African interior to "Christianity, commerce, and civilization," a trinity he believed would foster legitimate trade and help eradicate the slave trade. During his journey, he achieved significant feats, including the exploration of the Zambezi regions and the discovery of the waterfall he named Victoria Falls in honor of the Queen.1

Following his return, his book Missionary Travels and Researches in South Africa (1857) became a massive commercial success, selling over 70,000 copies and further elevating his fame. His subsequent lecture tour across the British Isles, including a notable address at Cambridge, inspired a new generation to continue his missionary and exploratory work in Central Africa.1