Anglo-Portuguese Alliance: The World’s Oldest Alliance

Written By Lara Silva

The Anglo-Portuguese Alliance is the world’s oldest alliance in known history, established by the Treaty of Windsor in 1386. The Portuguese and English alliance was signed on May 19, 1386, between the Kingdom of England and the Kingdom of Portugal. These two countries have always had a strong friendship throughout the centuries, dating back to 1147 when English crusaders helped King Alfonso I capture Lisbon from the Moors.

How was this alliance served both countries? The Anglo-Portuguese Treaty has made it so that these two kingdoms, later the United Kingdom and the Portuguese Republic, have never waged war against each other. This also includes never having participated in wars on opposite sides.

Both countries have helped each other during wars by exiling and providing refuge to individuals. This alliance was seen from the time of John Gaunt in the Middle Ages to the Peninsular War when the UK and Portugal held the lines against Napolean in Torres Vedras through to 20th-century wars. 

The Anglo-Portuguese Alliance was invoked during both World Wars. Portuguese military fought with the British in Europe and East Africa during World War I. In World War II, the Portuguese remained relatively neutral while giving the Azores Islands as bases for the Allied forces. 

The countries are also members of the North Atlantic Treaty Organization (NATO),  an intergovernmental military alliance between several North American and European states with huge military spending.

However, today, the UK and Portugal’s alliance goes beyond military cooperation. The alliance has flourished in the modern era to grow bilateral trade, foreign investment, and tourism. One could say the alliance has also impacted the expat relations between the countries, with both UK and Portuguese citizens immigrating to the countries. 

What is the Anglo-Portuguese Alliance?

The Anglo-Portuguese alliance officially started with the Treaty of Windsor in 1386. This diplomatic alliance was sealed by the marriage of King John I of Portugal to the daughter of John of Gaunt, Philippa of Lancaster. 

The alliance promises a union of friendship between the two nations, where these committed to never waging war against each other. This promise has been kept ever since. The Treaty of Windsor also stated that the two nations would provide aid to each other whenever necessary.

However, even before the Treaty of Windsor, the Anglo-Portuguese Treaty of 1373 took place on June 16. This treaty was signed between King Edward III of England and King Ferdinand and Queen Eleanor of Portugal. The treaty established a promise of mutual friendship, union, and alliance between the two kingdoms.

The treaty of 1386 is said to be a reinforcement of the first treaty in 1373, and a more official one. The alliance was further reinforced in 1643, 1654, 1660, 1661, 1703, 1815, and through a secret declaration in 1899. It was only officially recognized in the early 20th century in the Treaties of Arbitration.

However, the initial treaty of 1373 was made temporarily suspended from 1580 to 1640 during the Iberian Union. At the time, Portugal was briefly ruled by the Spanish, and the treaty with the British kingdom was void. However, even then the Portuguese exiled government looked for exile in Britain. When Portugal gained its independence, the alliance was back!

Importance of the Anglo-Portuguese Treaty

What is so important about the Anglo-Portuguese treaty? Let’s take a look at a summary of the importance and impact of the alliance between Britain and Portugal throughout history.

  • The Anglo-Spanish war (1585 – 1604) started five years after Portugal became ruled by the Spanish. The war between Spain and England began with England’s expedition to the Spanish Netherlands in support of the Dutch rebellion against Spanish rule. However, many say that England’s involvement in the war was also heavily aimed at getting Portugal its sovereignty due to the alliance.
  • During the Napoleanic Wars (1803 – 1815), Portugal was the only country in Europe to challenge Napolean’s blockade of British trade. This led Portugal to be invaded by Napoleon’s troops. Later, Britain’s biggest involvement in the wars was the establishment of a base in Portugal, from which they defended each other and even ventured into occupied Spain.
  • During World War I (1914 – 1918), Portugal joined the British on the side of the allies, sending soldiers to fight against German invaders.
  • During World War II (1939 – 1945), Portugal remained arguably neutral, keeping trade with both sides (although this neutrality is up for debate). Britain was okay with this neutrality, not wanting Spain to enter the war on the side of the Axis. In 1943, granted access to naval basis in the Azores to the British and later American troops. 

Portugal during World War II

Frequently Asked Questions (FAQs) 

What is the oldest alliance in the world?

The oldest alliance in the world that is still in force is the Anglo-Portuguese Alliance or the Treaty of Windsor of 1386 between the English and Portuguese Kingdom. These two nations, today the United Kingdom and Portuguese republic, stated they would never wage war against each other and would always provide aid to each other. This alliance is still valid today, making it the oldest continuous alliance in the world!

Why are England and Portugal allies?

Many Brits in particular wonder – why is Portugal Britain’s oldest ally? Their friendship dates way before the Anglo-Portuguese Treaty was signed. You could say it began in 1147 when English crusaders helped King Alfonso I capture Lisbon from the Moors. An English colony was then created in Lisbon and the two kingdoms remained connected ever since.

The Treaty of 1386 between Portugal and England then solidified this friendship. Throughout history, both of these nations protected each other from enemies and never once waged war against each other.

Does the Anglo Portuguese alliance still exist? Is the alliance still active?

The Anglo-Portuguese Alliance is the oldest alliance based in known history that is still in force by politics. The Treaty of Windsor was signed on May 9, 1386 between the Kingdom of Portugal and the Kingdom of England, over 630 years ago, and is still active to this day.

Want to learn more about the history of Portugal? Check out our History & Culture category with articles on various topics such as politics, revolutions, and iconic historical figures!
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