Anglo-Portuguese Alliance

The Anglo-Portuguese Alliance, ratified at the Treaty of Windsor in 1386, between England (succeeded by the United Kingdom) and Portugal is claimed to be the oldest alliance in the world which is still in force — with the earliest treaty dating back to the Anglo-Portuguese Treaty of 1373.

This alliance, which goes back to the Middle Ages, has served both countries. It was very important throughout history, influencing the participation of the United Kingdom in the Iberian Peninsular War, the UK's major land contribution to the Napoleonic Wars and the establishment of an Anglo-American base in Portugal. Portugal aided England (and later the UK) in times of need, for example, in the First World War.