The beginning of the colonial era in East Africa is not clear cut. The region started to fall under British influence since the first alliances of the Muscat sultanate with England, reinforced afterwards by Seyyid Said and prolonged during the Zanzibar sultanate. Apart from that ephemeral first British protectorate from 1824 to 1826, the European powers cultured their commercial relationships with the sultan. Both England and France attempted to dominate the trading routes with Asia. Since the Suez channel project was envisioned and forecasted to be the major highway for this trade, locating the Nile source meant controlling the river, and hence, the channel, reason why Uganda became a paramount objective. The channel would be opened in 1869 under French control, but in 1881 England would acquire most of the shares from an Egyptian citizen.

These economic and political interests found their counterpart in others, less tangible. For some, the exploration of Africa also posed personal challenges, being of epic or religious nature. Pioneers over all pioneers, the first Europeans to penetrate the unexplored inner lands of East Africa were two German missionaries serving the Church Missionary Society, which belonged to the Church of England.

Over centuries, caravans of Arab slave traders travelled into the continent for their supplies of human material. Tanganyika, today Tanzania, was the main source. The usual routes traversed the north of Tanzania towards the Great Lakes region, but always bordering Kenya. The reason? Fear of the Maasai, a hostile warring tribe that was the nightmare of every expedition. Until this golden age of African exploration was fully rolled out, all the Europeans breaking through the unexplored territories did so using the traditional routes that avoided the Maasai land, and the first incursions in this region were made under the protection of full armies. Except for Johannes Rebmann and Ludwig Krapf, the missionaries that, armed only with a sunshade and a Bible, were the first Europeans to explore the Kenyan inland.

In 1844, Johann Ludwig Krapf (1810-1885) established a mission in Rabai, in the outskirts of Mombasa, with the sultan's support. He was the first one to translate the Bible to Swahili and authored the first Grammar and Dictionary. In 1848 Johannes Rebmann (1820-1876) joined him. Both planned to take turns on a series of christianization expeditions into the continent. On May 11, Rebmann spotted the snowy summit of Kilimanjaro. Next year, on December the 3rd 1849, Krapf sighted, from what today is Kitui, another huge mountain, which the Kikuyu people believed to be the dwelling of their god Ngai and which they called Kima ja Kegnia, Kirinjaga, Kirinyaga or Kere-Nyaga (mountain of whiteness), from where the name of the country would later derive. The missionaries' descriptions were received with skepticism by the European scientific community, who judged it impossible to find perpetual snows around the Equator. The missionaries' observations were reflected in a map by a third missionary, Jakob Erhardt, who joined the Rabai mission in 1849. Based on his own experiences and on the Arab travellers' tales, he drew the famous "slug map", which in addition to the two mountains, showed a vast inland sea shaped like this mollusc.

Over the next years, Krapf repeated his expeditions, being the first European to explore the Tana river and to cross the Tsavo, the first to step on Yatta Plateau and to spot the Rift Valley. The missionary always considered himself a man of God rather than an explorer, since the aim of his journeys was not knowledge but christianization of the inland tribes. Sadly, the great success of his exploratory deeds was not matched by the results of his evangelizing task, which failed. Badly ill, Krapf finally returned to Europe, where he died frustrated for not succeeding in his goals.

One day, Rebmann received the visit of a man named Richard Francis Burton (1821-1890), a British officer who was planning, together with his friend and exploration mate John Hanning Speke (1827-1864), also an officer, to definitely unveil the secret of the Nile sources. Burton, a cultivated and documented adventurer, was familiar with Ptolemy's map and the missionaries' journeys. All the expeditions arranged so far in search of the Nile sources had departed from the mouth of the river in the Mediterranean Sea. All the explorers had been unsuccessful, dying disoriented in the midst of marshes and swampy jungles or turning back without accomplishing their mission. Burton had envisioned a route traversing the continent from the east coast, but his first try from Somalia in 1855 had failed after a bloody attack from the natives in which Burton himself got seriously injured. Rebmann handed the "slug map" to Burton and advised him to cross the Maasai land, probably the shortest way. But Burton and Speke had also heard the stories about the Maasai, and so they rather chose the south route, following the paths of the Arab slave traders.

The expedition departed from Zanzibar on the 17th of June 1857, with the help of Sidi Bombay, a Swahili guide that would become indispensable in African exploration, since he would later guide two of Stanley's expeditions. After a long and arduous journey overburdened with disease, robbery and desertion, on the 14th of February next year Burton and Speke became the first Europeans to set their eyes on Lake Tanganyika. By then, Burton was unable to walk due to malaria and Speke was virtually blind as a result of an infection. Versions differ regarding what actually happened afterwards, mainly due to the enmity risen by such opposed personalities, which is reflected in inconsistencies between different chronicles. It seems clear that Burton remained in Tabora, an inland city famous for its active slave trade, while Speke marched alone northwards and reached a vast lake, which he named Victoria in honour of his Queen. From the start, Speke presumed the lake to be the Nile source, but he did not locate the stream. Burton, either more rigorously scientific or jealous because of his now-enemy's success, never recognised the discovery. After the journey back to the coast, Burton stayed at Zanzibar, while Speke returned to London and proclaimed himself as the discoverer of the Nile source. Burton was never honoured and in his work Lake Regions of Central Africa (1860) he erroneously proposed the Tanganyika as the one and only source of the Nile.

Speke travelled back to Lake Victoria in 1860, with the support of the Royal Geographical Society and accompanied by his friend James Augustus Grant. The two explorers were received in what today is Kampala by the kabaka or king of Buganda, Mutesa I. There they were informed that a big stream surged eastwards from the north lake shore. Speke sent Grant to study the way back downstream towards the Mediterranean while he monopolized the great finding, a small cataract which he named Ripon Falls, where the lake overflowed to give birth to the large river. Speke joined Grant downstream to Khartoum, from where he sent a dispatch to London giving account of his discovery: "The Nilo is settled". Nonetheless, Speke never contributed enough evidence to support his hypothesis: the journey downstream could never be fulfilled due to clashes with the natives.

During the journey back, Speke and Grant met another English expedition in Gondokoro, led by Samuel Baker and his fiancée Florence von Sass. Speke told them about the possible existence of another great lake west of Victoria. Baker and von Sass followed Speke's indications and thus reached in 1864 Lake Albert, which is part of the Nile course along its way northward.

The bitter controversy between Burton and Speke was brought to the public light. In 1864 the British Association for the Advancement of Science organised what was known as "the Nile duel", in which both explorers were invited to present and discuss their respective theses. The debate would never take place. Speke died that very day in a weird hunting accident, which some judged to be suicide due to the pressure and fear to face his former friend, very superior in the art of debate.

David Livingstone (1813-1873), Scottish missionary and father of African exploration, was famous while alive, loved and admired by the Victorian society both for his discoveries in Central Africa and for his main motivations, bringing the word of the Christian God and the western civilization to the natives, as well as abolishing the slave trade. He seeked the source of the Nile, though his most important findings were located more southward. Among them were Victoria Falls in the Zambezi, named by Livingstone in 1855. At the end of his third and last African expedition, Livingstone was in Ujiji, at the east coast of Lake Tanganyika, aged and almost paralysed by hemorrhoids. Meanwhile, in Europe, anxiety about Livingstone's whereabouts grew stronger. And so it was that in 1869 a Welsh journalist who had emigrated to the United States, Henry Morton Stanley (1841-1904), was sent by the New York Herald in search of Livingstone. The journalist located him in Ujiji in October 1871. Livingstone, recovered from his illness, accompanied Stanley on some of his explorations north of Tanganyika, but he refused to return to England with him. Loyal to his passion, Livingstone set out on a new journey southward and died in Chitambo, in what today is Zambia, on the 1st of May 1873. The cause of his death was hemorrhoids, for which he had repeatedly refused surgery. An absurd end for a mythical figure that survived thousands of dangers.

Stanley was Livingstone's opposite: racist, ambitious and unscrupulous. Despite, both developed a keen friendship, to such an extent that, upon Livingstone's death, Stanley resolved to resume his exploratory labour. There were still plenty of geographic secrets to unveil, among them the confirmation of the Nile source in Lake Victoria. Funded by the New York Herald and the Daily Telegraph, Stanley departed from Zanzibar in November 1874. His visit to king Mutesa I of Buganda opened up the doors to the Christian missionaries and set the basis for the establishment of a British protectorate in Uganda. Stanley circumnavigated Lake Victoria, which allowed him to corroborate Speke's hypothesis, checking also the connection with Lake Albert. He confirmed that there was no connection between Tanganyika and Victoria, refuting Burton. Determined to put an end to the discussion, Stanley also refuted Livingstone's theory which proposed the Lualaba as part of the Nile system upstream Lake Victoria. Stanley showed that the Lualaba is actually a tributary of the Congo, which he sailed downstream to its mouth at the Atlantic Ocean. On the 12th of August 1877, Stanley would become the second European to cross Africa from ocean to ocean, few months later than the explorer Vernon Cameron. His second journey was recorded for posterity in 'Through the Dark Continent' (1878).

Stanley kept on travelling through the Congo territory, this time on behalf of the king of Belgium. But one more final deed was awaiting him: in 1887 he received an offer to rescue Emin Pasha, a German Jew and British subject who had worked as a mercenary for jedive Ismael of Egypt, who had appointed him as governor of the Egyptian province of Equatoria, at the source of the Nile, with England's approval. An uprising promoted by the Islamic fundamentalist leader El Mahdi, in Sudan, isolated Equatoria from the rest of Egypt, threatening the Egyptian domination in the region and even the governor's life. Stanley came to release Emin Pasha, but just to discover that he did not wish to be released, since he had taken advantage of the circumstances to declare the independence of Equatoria. Despite, Stanley had a mission, and he drove the reluctant Pasha to Zanzibar.

Emin Pasha's rescue was a novelesque adventure, as famous at the time as the rendez-vous of Stanley with Livingstone. However, apart from its epic character, the trip would provide new findings for Stanley. His steps led him to Semliki river, which connects lakes Edward and Albert, being part of the Nile system. But even more important, Stanley could at last close the circle: he spotted the peaks of the Ruwenzori Range, the Mountains of the Moon. Hidden amidst the clouds for the most time, the snowy summits had passed unnoticed first for Samuel Baker and later for Stanley himself in his second journey. The snows up the Mountains of the Moon finally resulted to someway feed, as had always been believed, the sources of the Nile.