Final answer:
The Samoan Protectorate ended in 1899 with Germany annexing Samoa after an agreement with the United States and Great Britain, who divided the islands among themselves.
Step-by-step explanation:
The Samoan Protectorate ended in 1899 when Germany, Britain, and the United States formally agreed to divide the Samoan islands. The agreement resulted in Germany taking control of the islands now known as Samoa, and the United States receiving those now called American Samoa.
Great Britain withdrew its claim on the Samoan islands in exchange for control over some of Germany's territories in the North Solomon Islands and concessions in Africa. Therefore, the correct answer to the question is Germany annexed Samoa as part of the tripartite agreement, with the United States also taking control of part of the islands.