Invasion of their lands, hard work conditions, unfair colonial laws, a discriminatory social system and abusive taxes engendered among the natives a logical resentment towards the Europeans, and fed the seed of African nationalism. Maasais and Kikuyus were the most affected, for they were the tribes that had traditionally inhabited the region were Nairobi was founded. The Maasais chose not to mix their destiny with that of the foreigners and accepted retiring from the scene, but Kikuyus remained beside their former lands and were exploited as basic manpower source.

On the other hand, a handful of Europeans, concerned about the natives' future and the despoilment that was going on, started to raise their voices to express their disagreement with the course of colonial policies. Already in the early 1910's, Karen Blixen's effort to school the Kikuyu children was received with a mixture of skepticism and distrust by the most recalcitrant. Winston Churchill, a conservative and a convinced colonialist, wrote after an official visit to Kenya in 1907, when he was Secretary of State for the Colonies, that he did not believe in the myth of the "white man's country", and that education and comprehension should drive an increase in the native tribes' standard of living. The English government's official view, expressed in the Devonshire Declaration in 1923, accepted the need for developing the African interests. Even Meinertzhagen, who authored the massacres against the Kikuyus, changed radically when later on became, as years passed and maybe by the weight of guilt, a passionate defender of African nationalism. However others, like Delamere, believed in a white Kenya till the end of their lives.

A conscience of nature conservation also rose in those days. Until then, only specially sensitive figures such as Livingstone had showed concerns in this sense. Confronted to the wildlife massacres performed without ceremony by many settlers and visitors, including Theodore Roosevelt and Ernest Hemingway, some professional hunters like Denys Finch-Hatton, Phil Percival or Frederik Selous, started to wonder about the impact of their activity on African wildlife, reckoned that animals would not last forever and even became very selective in their shots, criticizing the attitudes of those bloodthirsty butchers whose only will was to produce the highest fleecing of wildlife during their hunting expeditions. The Hunters Association, founded in 1920, dictated restrictive rules that caused complaints from those that still believed in the free and endless hunting grounds. Meinertzhagen wrote about the nonsense of those creatures, hardly more intelligent than elephants, murdering these magnificent animals just to play billiard with balls manufactured with their tusks. Later, in 1946, the conservation conscience would result in the gazetting of Nairobi National Park, followed two years later by Tsavo.

The natives' discrimination, even towards other races different from the white, was patent in all aspects of colonial life. In 1927 the elected representatives of Arabs and Asians entered the Colony Legislative Council. Conversely, African interests were represented by a white settler designed to do so. At the public premises there were toilets for European gentlemen, European ladies, Asian gentlemen and Asian ladies, but none for Africans.

African nationalism was born during the early colonial times. Kikuyus hid in the forests, away from the whites' hunting grounds, and organised societies which were ignored by the colonial rulers. In the 1920's several political organisations started up, such as the East Africa Association and the Kikuyu Association.

In 1921, one of the first leaders, Harry Thuku, founded the Young Kikuyus Association. One year later, in March 1922, Thuku was arrested by the colonial police. This was the spark that triggered the first large uprising. The Kikuyus revolted outside the police station were Thuku was confined, in front of Norfolk Hotel, and both police and settlers replied with violence. The clash was resolved with 21 dead and Thuku was deported to Kismaiyu, where he remained until 1931.

In the late 1920's a decisive figure in Kenya's history started to emerge. His name was Johnstone Kamau Wa Ngengi (1892-1978), son of peasants and better known as Jomo Kenyatta, called Mzee, the Venerable. He was born between 1892 and 1893, probably in the village of Ichaweri or otherwise in a town near Kiambu, in the Kikuyu country. He received baptism by the Kikuyu and Christian rites. He was educated by the European missionaries and when he was 29 years old he settled down in Nairobi to work as a translator. His involvement in the fight for the natives' rights since 1920 drove him to affiliate to the East Africa Association, and to later assume in 1924 the general secretariat of the Kikuyu Central Association. In 1929 he was sent to England to report on the colonial administration's abuses. He was not listened and started a pilgrimage all around Europe, along which he learnt politics and became the uncontested leader of Kenyan nationalism. From 1931 to his return to Kenya in 1946 he lived in England, where he studied linguistics and anthropology, affiliated to the labourist party and worked as a University teacher. In these days he published two books, 'Facing Mount Kenya' and 'Kenya - land in conflict' (1945).

Meanwhile, other political events were configuring the country we know today. In 1920, the Colony of British East Africa finally became the Kenya Colony. In 1926, the west shore of Lake Turkana, until then under the Kampala administration, was integrated into the Kenya Colony, defining the country's present-day boundaries.

The early 1930's began with the extension of demonstrations throughout the country, as well as an increase in political activism by the natives. The powder keg was about to blow up. Different associations appeared at the local level, like the Taita Hills Association.

When World War II broke out, many Africans were recruited to fight with the allied troops. Kenyans then discovered that Europeans were also vulnerable, that they could fight and die same as them. Africans' involvement in great war deeds served to feed their wrecked pride as a people. Once back home, it was hard for them to find that life conditions in their huts were worse than what they had found in the barracks.

On October the 5th 1944, an African was finally admitted to the Colony's Legislative Council. Eliud Mathu was not elected by suffrage, but appointed by the Europeans. In order to support him, the first political organisation at the national level was created, the Kenya African Study Union, later re-named Kenya African Union (KAU).

With the end of the conflict, the United Kingdom assumed the need for re-shaping the empire into a community of self-governed countries, and thus the Commonwealth was born. The aim was double: on one hand, to gain the support of the small emergent countries in Africa, Asia and South America against the communist block. On the other hand, to revivify their domination at the time when the empire in Asia and Near East was starting to crack. Since East Africa was considered an economic and strategic base, the High Commission for East Africa initiated a process of federative union, in an attempt to homogenize currency, institutions and customs.

The reforms did not arrive and atmosphere grew more tense. From 1947 to 1948, 11,000 Kikuyus were thrown away from their lands. The natives' struggle diverged in two groups, those who defended a political way and those who opted for unconditional violence. Among the former was Jomo Kenyatta, who returned to the country in 1946 and assumed the leadership of KAU in secrecy. For the next six years he practiced an intense and tireless political activism.

The violent faction was gaining support with each new brutal police action. The first organised groups were initially gangs of criminals devoid of political background, who controlled illegal traffic of alcohol and drugs. These groups, who were familiar with the methods of organised crime, received the political inspiration from Kikuyu veterans, and in 1946 the Forty Group was created in Banana Hill, under the leadership of Fred Kubai and Bildad Kaggia, who launched a terrorist campaign of opposition to the colonial regime. They named themselves the Freedom Fighters. They celebrated secret initiation ceremonies, executed those who refused joining them and committed robberies to gather weapons for their activists. Their main secret agents were the Nairobi and Mombasa prostitutes, who switched from charging money to perform their sexual jobs in exchange for ammunition. The Forty Group would be, hardly one year later, the seed of the violent Mau-Mau guerrilla.