The German–Spanish Treaty of 1899, (Spanish: Tratado germano-español de 1899; German: Deutsch-Spanischer Vertrag 1899) signed by the German Empire and the Kingdom of Spain, involved Spain selling the majority of its Pacific possessions not lost in the Spanish–American War to Germany for 25 million pesetas (equivalent to 17 million Marks) During the 19th century, the Spanish Empire lost most of its colonies to independence movements.

Cuba became independent while the United States took possession of Puerto Rico along with the Philippines and Guam from Spain's Pacific Ocean colonies, the Spanish East Indies.

It has been asserted that some islands (Kapingamarangi, Nukuoro, Mapia, Rongrik, Ulithi, and "Matador", probably a reef already sunken today, but it appeared on maps of the time) are still in Spanish possession since they were not transferred to the United States nor to Germany.

The hypothesis appeared on 5 March 1948, when the state lawyer and CSIC researcher Emilio Pastor y Santos wrote a letter claiming that Spain should establish three naval stations in the Carolinas, Marianas and Palaos, following article 3.

On 12 January 1949, the question was dealt with in the Council of Ministers, but ...while the subject is not clear, it becomes to wait before dealing with the United States or the friendly powers taking part of the United Nations, since Spain has no contacts with the UN and it would be this organization which would solve the final lot of those Micronesian islands owned by Japan.However, a report of 4 January 1949 from the legal advice of the Spanish Ministry of Foreign Affairs "estimated that any hypothetical right of Spain over those islands would have been destroyed by the later trust regimes, that were those established after World War I with the transfer of those territories to Japan and, after World War II, with their attribution to the United States".