What has a small island in the North Sea, 40 km off the German coast, got to do with Africa?
The island of Heligoland had been under British rule since 1807 when they seized it from the Danes. As a base for naval operations it would prove very important and the German Chancellor, Bismarck, had set a priority on obtaining it. In July 1889 the German ambassador in London, Count Hatzfeld, visited the British prime minister, the Marquess of Salisbury, to open negotiations. Salisbury was worried about the security of British colonies in East Africa -- Germany was making a bid for lands to the north and south of its current holdings -- and Heligoland proved to be a suitable bargaining chip.
Why was Britain worried over East Africa?
Since the Berlin conference, 1884--1885, Europe had been 'scrambling' for African territories. In East Africa Britain had staked a claim to the mainland north of Zanzibar, intending to connect up to the Anglo-Egyptian Sudan. The German explorer Carl Peters had been efficiently collecting treaties in the region to the south and a German protectorate had been declared. Germany also had a (small) claim to the north along the coast between Witu (at the estuary of the Tana River) and Kismayu (in what is now Somalia).
In 1889 however, things came to a crisis when Carl Peters headed north on the German Emin Pasha relief expedition. Failing to secure Emin Pasha's safety -- Henry Morton Stanley had got there first -- he decided to go hunting for territory instead. News had reached him that King Mwanga of Bugunda (Uganda) was looking for help to re-claim his throne, offering treaties with anyone who would help. Peters took the initiative and beat British representatives to the prize. If Germany was successful in creating a protectorate they could potentially join it up with their colony at Witu and cut off the connection between British East Africa and the Sudan! In addition to Germany's territorial expansion in the north, missionaries and traders in Nyasaland to the south (part of the future British Central African protectorate), especially that part between lakes Tanganyika and Nyasa, were worried that Germany intended to expand south, increasing their land claims.
What was the Heligoland Treaty?
In return for the island of Heligoland the British Prime Pinister, Salisbury, demanded several things: that Germany recognise the British protectorate over Zanzibar and Pemba (previously a semi-independent Sultanate), that Germany renounce its claims to the regions of Witu and Uganda (a clause which aggravated Carl Peters tremendously), that Britain have access between Lake Tanganyika and Uganda, and that Germany leave the region to the west of Lake Nyasa to Britain. Despite the Kasier's overwhelming desire to obtain Heligoland, the German ambassador, Count Hatzfeld, managed to obtain a few concessions.
The frontier was to run parallel to 1°S west of Lake Victoria until it met the Congo Free State border - this effectively blocked a continuous 'Red Route' of British holdings from the Cape to Cairo. (Britain was unable to persuade King Leopold to give them access rights through the Congo Free State because of protest by Germany and France.) To the east of Lake Victoria the border was to run in a straight line to the coast, to a point opposite the island of Pemba. In addition Germany obtained a narrow strip of land extending from German South West Africa (now Namibia) to the Zambezi River, to be known as the Caprivi strip (named after the German Chancellor at that time). The treaty was ratified on 1 July 1890.
What was unusual about the Heligoland Treaty?
The most Euro-centric aspect of this treaty was that Queen Victoria insisted that her grandson, the German Kaiser Wilhelm II, be given a mountain in Africa - Britain had two, Germany had none. So the border from Lake Victoria to the coast has a kink in it, putting Mt. Kilimanjaro in German East Africa (now Tanzania).