Anglo-Portuguese Treaty of 1373 Anglo-Portuguese Treaty of 1373 The Anglo-Portuguese Treaty of 1373 was signed on 16 June 1373 between King Edward III of England and King Ferdinand and Queen Eleanor of Portugal. It established a treaty of "perpetual friendships, unions [and] alliances" between the two seafaring nations. It is the oldest active treaty in the world. It was confirmed "with my usual flourish" by John de Banketre, Clerk. It was reinforced throughout history, including in 1386, 1643, 1654, 1660, 1661, 1703, 1815 and by a secret declaration in 1899. It was recognized in the Treaties of Arbitration in the 20th century between Britain
Secret treaty financial arrangements, and 'military understandings'" are commonly cited as one of the causes of World War I. For example, the Reinsurance Treaty of June 1887 between the German Empire and the Russian Empire (negotiated by German Chancellor Otto von Bismarck in order for Germany to avoid a two-front war), was a "highly secret treaty" in which the two powers pledged a three-year period to remain neutral should the other become involved in a war with a third country, unless Germany attacked Russia's longstanding ally France or Russia attacked Germany's longstanding ally Austria-Hungary. The use of "secret agreements and undertakings between