By the beginning of the study period, East Africa (Kenya, Tanzania, Uganda, Burundi, Rwanda) had already been settled by Bantu language-speaking, iron-working agriculturists. During the early part of the study period, infusions of genes occurred from lands to the north by land and sea.
Third to sixteenth centuries - Immigration of Nilotic peoples: The southern Sudan is the ancestral home of the Nilotic peoples (non-Bantu). The Nilotes are traditionally cattle herding semi-nomads, and are responsible for the importation of many cattle herding practices into East Africa. Starting in the third century, a series of major Nilotic migrations into the highlands of Uganda, Kenya, Tanzania, Rwanda, and Burundi began. In many cases, the Nilotes assimilated with local peoples, adopting Bantu languages. In some, notably the Luo, Maasai, Samburu, Turkana, Teso, Hima, Tutsi, and Karamojong peoples, they have remained determinedly distinct. Among their achievements were the founding of the Bunyoro and Buganda kingdoms of Uganda. In any case, if your ancestors were living in the highlands of East Africa in CE 1800, it is probable that at least some of their ancestors were in southern Sudan at earlier times, especially if they are from the peoples indicated above.
Fifth to Fifteenth centuries - Swahili culture: Trade between the Middle East and communities on the East African coast was in place since before CE 1. With the rise of the Umayyad Caliphate, this trade increased, with Arab and Iranian traders settling in town like Mogadishu, Lamu, Mombasa, Pemba, and Zanzibar, marrying locals, and coordinating trade with the relatives back home. The ultimate result was the rise of Swahili culture - Islamic in outlook but primarily African in personnel. The Kiswahili language reflects their character - Bantu in essence but with many Arabic words. Nevertheless, if your ancestors lived in the coastal towns of East Africa in CE 1490, their ancestors probably also lived in Arabia, Iraq, or Iran in earlier periods, also.
The Swahilis both traded with the interior for forest products and raided the interior for non-Muslim captives that formed their labor force and later, became a major export item. Thus, your Swahili ancestors of CE 1490 may also have had ancestors in the interior.
The Sixteenth Century - Portugal attacks: When the Portuguese developed sea routes to the Indian Ocean, they discovered the rich Swahili trade with the Middle East and sought to coopt it. One by one, Swahili towns fell to their attacks and became hosts to Portuguese garrisons and forts. Thus, your Swahili ancestors of CE 1800 may also have had ancestors in Portugal in CE 1490.
Eighteenth and Nineteenth Centuries - society breaks down: By and by, human captives became a major item of export by Portuguese and (after they had been ejected from the Swahili towns north of Mozambique) Arab and Swahili traders. These were mostly taken from Uganda, and western Tanzania and shipped to the French colonies of Mauritius and Reunion, or to Brazil. Still, many were for "domestic consumption" in the Swahili cities. As the slave trade intensified in the early nineteenth century, East and Central African communities were severely disrupted. Almost as bad was the trade in ivory, in which innocent people were captured by ivory traders for use as porters or held until a ransom of elephant tusks was paid. These disruptions persisted through the 19th century. If your ancestors lived in Burundi, Rwanda, the interior of Tanzania or in southern Uganda in CE 1900, their ancestors could have been from anywhere there or in adjacent parts of Central Africa in CE 1800 and CE 1490.
Late nineteenth century - colonization: The disruptions of the slave and ivory trade were an invitation for Western powers to step in, restore order, and manage the export trade. Thus, Kenya and Uganda became British colonies, and Tanzania, Burundi, and Rwanda German (later British and Belgian). Although there was little intermarriage between colonists and locals, it was not unheard of. Your family folklore and the evidence of your senses will inform you.