This is proof of the constant commitment of the two nations over the centuries to support each other, namely that the Anglo-Portuguese alliance is still a valid agreement that has been approved by both countries and will undoubtedly exist in the future. The title says just about everything. What is the oldest treaty (of what kind) still imposed between two political entities (nation states, cities, etc.)?  House of Commons Debate, October 12, 1943, vol. 392 cc716-19, published in hansard.millbanksystems.com/commons/1943/oct/12/agreement-with-Portugal It was reactivated during World War II, after which the Portuguese remained neutral, in agreement with Great Britain, who did not want to bring war to the Iberian Peninsula. This lasted until 1943, when, after three months of negotiations, it was completely reactivated by the national government of Winston Churchill and Portugal.  Britain has received airfields and nautical facilities in the Azores of Portugal to combat the threat of submarines. The British also cited the treaty during the Falklands War in 1982. The Luso-British Alliance, ratified in 1386 with the signing of the Treaty of Windsor, marks the oldest active political treaty in the world. The treaty signed between the Kingdom of Portugal and the Crown of England provided mutual military assistance in the face of aggression by foreign troops. Certainly the oldest military alliance, but not sure that there are others. The first point is that Portugal is in fact England`s oldest ally. It is only because England is now part of the United Kingdom that Portugal is considered a British ally. This agreement would provide a strong information on how the coherent foreign policy of the two nations was conducted.
For example, Britain sent military support to Portugal when Spain invaded the country in 1762 and then helped repel Napoleon`s attempts to conquer the Iberian country. At the same time, during the First World War, Portugal sided with the United Kingdom and supported Britain`s efforts during the 1981 Falklands War with logistical support of its military bases in the Azores. A treaty is a binding agreement between EU member states. It sets out the EU`s objectives, the rules for EU institutions, how decisions are taken and the relationship between the EU and its member states. The parage of Andorra was a feudal charter signed in Lleida on September 8, 1278. It codified a lay and ecclesiastical agreement between the Earl of Foix, Roger Bernard III, and the Bishop of Urgell, Pere of Urtx, and based their common sovereignty over the territory of Andorra. The Anglo-Portugese Alliance is the oldest ongoing alliance in the world, dating back to the Windsor contract of 1386. The Anglo-Portuguese Alliance (or Aliana Luso-Inglesa, „Luso-English Alliance“, ratified by the Treaty of Windsor in 1386, between the Kingdom of England (since the successor of the United Kingdom) and the Kingdom of Portugal (now the Portuguese Republic) is the oldest alliance based on the well-known history of the world and still in force by politics – with the oldest treaty, dating back to the Anglo-Portuguese Treaty of 1373. On 9 May 1386, the initial draft (protocol) of the treaty was drawn up and ratification of the treaty was included in the archives of „contractual roles“ at the Chancery (National Archives: C 76/71 m.9). However, the revolution of 1820 in Portugal triggered a thirst for independence and the outbreak of armed conflicts in Brazil.
The event transformed British policy towards the recognition of an independent Brazil.