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650 years: The Anglo-Portuguese Alliance between England and Portugal

Authored by Rex Cleaver
Published on 16th June, 2023 17 min read

650 years: The Anglo-Portuguese Alliance between England and Portugal

Marriage of King John I of Portugal to Philippa of Lancaster, 14th February 1387 650 years ago today (16/06/2023), King Edward III of England and King Ferdinand and Queen Eleanor of Portugal agreed the Anglo-Portuguese Treaty, establishing a formal alliance that has since become the longest continuous peace treaty between two nations in history. As centuries passed, these nations amassed vast colonial empires that benefited from joint trade and security agreements. England and Portugal thus developed a partnership characterized by shared values, strategic interests, and mutual support. 

The origins of this ancient alliance lie even further back in history: during the 12th century. Then, English crusaders, enroute to the Holy Land during the Second Crusade, stopped off in Portugal to assist their fellow Christians during the Siege of Lisbon in 1147. [1] Having aided in bringing the city of Lisbon under Christian control, the Kingdom of England had demonstrated its usefulness to its European sister, laying the foundations for a relationship that has spanned over half a millennium. 

Formally ratified on the 9th of May 1386 via the Treaty of Windsor, the marriage of King John I of Portugal to Philippa of Lancaster bound the two countries together in dynastic union. Philippa was the daughter of John of Gaunt, the famous Duke of Lancaster, who had already made an earlier abortive claim to the Kingdom of Castile through his marriage to Constance of Castile. The Duke’s failed attempt at the throne was just one manifestation of long-running English interest in the region. The Duke’s aspirations were understandable: the Crown of Castile exerted significant influence and its military capability was demonstrated repeatedly during the many conflicts known as the Hundred Years' War (1337−1453).

The Treaty of Windsor sealed on 9th May 1386 (The National Archives: E 30/310) Castile’s earlier alliance with France (1369) threatened both the independence of Portugal and caused considerable consternation in the English court. With France gaining access to the Kingdom of Castile’s enormous fleet of warships, England’s dominance over the seas would be brought into serious question in the case of a potential conflict. [2] Tensions were stretched to a breaking point in 1383 by the death of King Ferdinand I. His death initiated a succession crisis which quickly led to civil war. This period (1383−1385), which has since been given the slightly mundane moniker “The Portuguese Interregnum”, culminated in the Battle of Aljubarrota (1385), where the Kingdom of Portugal and the Crown of Castile finally came face to face on the battlefield. 

Battle of Aljubarrota, 1385Honouring the alliance of 1373, Richard II of England sent over a small garrison in support of John of Aviz (later John I), the leading claimant to the Portuguese throne. The garrison consisted of 200 longbowmen, mercenaries and other veterans of the Hundred Years’ War, as well as 500 locally recruited men-at-arms. This small but significant force played a crucial role in the conflict. English tactics, learned during the ongoing Hundred Years War, were employed throughout the battle thereby ensuring the defence of the Portuguese troops against Castile’s army. [3] Having defeated the Castilians, John of Aviz’s victory ruled out Castilian ambitions for the Portuguese crown and secured his place on the nation’s throne. 

Indebted to the English forces and finances that had helped keep his royal ambitions afloat, John I of Portugal duly accepted Philippa of Lancaster as a bride, cementing the Anglo-Portuguese alliance. The Treaty of Windsor put into writing a pact of perpetual friendship between the two nations, promising mutual aid, trading opportunities, and military support. Perhaps the most important excerpt from the Treaty reads:

It is cordially agreed that if, in time to come, one of the kings or his heir shall need the support of the other, or his help, and in order to get such assistance applies to his ally in lawful manner, the ally shall be bound to give aid and succour to the other, so far as he is able (without any deceit, fraud, or pretence) to the extent required by the danger to his ally’s realms, lands, domains, and subjects; and he shall be firmly bound by these present alliances to do this. [4]

Now wedded to the King of Portugal, Philippa dutifully embodied the ideas of the Treaty, providing royal patronage for England’s commercial interests and bringing Anglo-Norman ideas and reforms to the Portuguese court. Becoming one of the country’s best-loved queens, she became the first in what was to be known as the “illustrious generation”, a proud name given by the Portuguese to Philippa’s children. 

Having enjoyed a relatively peaceful and prosperous relationship for centuries, the alliance between the two countries suffered its most significant hiccup almost two hundred years later, during the Iberian Union (1580-1640). This saw Portugal subsumed into the Spanish Empire following the dynastic union of the Crowns of Castile and Aragon and the Kingdom of Portugal, thereby unifying the Iberian Peninsula. Portugal had suffered yet another crisis of succession and unlike the Interregnum that had occurred two hundred years earlier, this later crisis failed to produce a successful claimant to the throne. While many nobles threw their hat in the ring, chiefly António, Prior of Crato, the Portuguese claimant and his forces were no match for Philip II of Spain. Philip crushed the pretender’s troops at the Battle of Alcântara (1580) seizing the Portuguese throne soon after. 

Relationships between England and Portugal inevitably came under strain as Portugal, now a part of Habsburg Spain, was forced to consider England as one of her enemies. António, paranoid that he would be assassinated by Philip II, escaped to England after being granted refuge by Elizabeth I. There, he attempted to raise local support for his claim on the Portuguese throne. Elizabeth I, bolstered by the recent English success against the Spanish Armada (1588), agreed to a retaliatory attack against Spain and launched a “Counter Armada” in 1589 under the command of Sir Francis Drake and Sir John Norris. António accompanied the expedition with the promise that he would be installed on the Portuguese throne once the armada had landed at Lisbon. While the Prior of Crato’s nationalist movement had the support of both France and England, the “Counter Armada” failed on all fronts, decimating the financial resources of England’s treasury. Hoping in vain that the citizens of Lisbon would rise and support his cause, António’s English backers were, crucially, Protestant. As Edgar Prestage has highlighted, while the citizens of Lisbon “had little love for Spaniards, they had less for heretics and felt resentment towards the nation which had intruded itself into their colonies.” [5] With its financial and military reserves severely depleted, England was forced to step back.

The humiliating failure of the English Armada to trigger a Portuguese uprising meant that England’s alliance with Portugal continued to be held in abeyance until 1640 when the Portuguese Restoration War put an end to the Iberian Union. This enabled the two countries to reignite their alliance, reaffirming the treaty again in 1643.

The most famous period of collaboration between the two countries was during the Peninsula War (1807-1814), part of the ongoing Napoleonic Wars then ravaging and reshaping continental Europe. Napoleon was furious that Portugal had refused to join the Emperor’s Continental Blockade, a large-scale embargo that effectively stopped Britain from trading with Europe. [6] Portugal, honouring its centuries-old alliance with Britain, openly refused to join the blockade and continued to trade with its ally, even allowing British ships to use its port in Lisbon as a military base. Unable to force Portugal to cease its trading ties with Britain, Napoleon decided on a more direct approach and swiftly invaded the country, initiating the Peninsular War.

Britain’s decision to intervene in the conflict precipitated a long and bloody campaign aimed at increasing British military power in mainland Europe and driving the French out of Portugal and Spain.[7] Led by Lieutenant-General Sir Arthur Wellesley (later to become the Duke of Wellington), 15,000 British troops landed in Portugal in August 1808. Having established a military base in Portugal, Wellesley and his troops pushed back surrounding French forces, first at Roliça on the 17th of August 1808, and again at Vimeiro just four days later, thus ending the first French invasion of Portugal. 

With the French driven out of Portugal, Wellesley realised that it was only a matter of time before Napoleon would attempt another invasion, determined as he was to bring the entire peninsula under French control. Wellesley ordered extensive fortifications be built across Portugal, ensuring Lisbon’s protection in the case of another invasion. Taking several years to complete, 152 fortifications and 648 cannons marked out the defensive lines that had been carved across the Portuguese hills and mountaintops, scarring the land with redoubts, escarpments, and roads that allowed troops to move quickly between fortifications. To this day the Lines of Torres Vedras still cover the landscape, their overgrown remains standing as a powerful reminder of an alliance that was already over 400 years old by the time of the Peninsula War.

With the Lines of Torres Vedras aiding Wellesley in holding off numerous French attacks after 1808, a couple of years later in 1813, Wellesley decided to go on the offensive, marching 120,000 troops from Northern Portugal to the mountains of Northern Spain. Meeting Joseph Bonaparte — brother of Napoleon and recently crowned King of Spain — at the city of Vitoria, the heart of Spain’s Basque County, Wellesley led a combined army of British, Spanish, and Portuguese servicemen. Splitting his army into four columns, Wellesley's forces drew the French into a defensive position, forcing them to pull back towards Vitoria. After hours of heavy fighting, the French were defeated, retreating towards Pamplona. Following the victory of Vitoria, Joseph Bonaparte’s reign over Spain came to an end. Most of Bonaparte’s followers fled to France, along with the retreating military and Joseph promptly abdicated. 

The Battle of Vitoria, 1813The Peninsular War was one of the bloodiest wars in Spanish history. With the entire country ravaged by conflict, Portugal’s position on the continent had now become the more favourable of the Iberian nations.[8] It had avoided the worst of the fighting, with the Lines of Torres Vedras stopping incoming French attacks from getting past the Northern territories. Much to its British ally’s pleasure, it also continued to maintain its colonial power in Brazil, a country that Britain was keen to increase its investments in. Indeed, the British Royal Navy had escorted the Portuguese Royal Family to the safety of their viceroyalty in Brazil at the onset of the Peninsula war. Evidently, the British were keen to ensure that their privileged trading positions with the colony remained intact.[9]

While the Anglo-Portuguese Alliance had been reaffirmed by the aid provided by the British during the Peninsula War, as explained by Lord Palmerston, Britain has “no eternal allies, and we have no perpetual enemies. Our interests are eternal and perpetual, and those interests it is our duty to follow.” [10] While Britain had sacrificed thousands of men to ensure Portugal retained its independence, the alliance continued unabated with Britain safe in the knowledge that its commercial interests in Europe and South America would continue to grow in the nineteenth century as its Empire reached its apotheosis.

The commercial and colonial interests that underpinned the Anglo-Portuguese Alliance were most obviously illustrated in 1890 when the British government issued the Kingdom of Portugal with an ultimatum. Portugal wanted to acquire territory in British Rhodesia, which now lies in Zimbabwe and Zambia. With Portugal having established colonies in Angola and Mozambique, acquiring this land in central southern Africa would effectively connect a corridor of land and so form a prospective trade route across the continent. 

Initially assuming that Britain would treat its long-term ally favourable during the scramble for territory in Africa that occurred during the nineteenth and early twentieth centuries, Portugal was surprised to discover that Britain outright rejected the idea of an expansion of Portuguese influence in Africa, particularly when it meant giving up land. Britain was already dealing with the ongoing question of Irish Home Rule and with the Empire at the height of its colonial power, was loathe to start giving up vast quantities of land. [11] An ultimatum was subsequently delivered by Lord Salisbury, demanding Portugal withdraw their troops from the regions in Africa where Portuguese and British interests overlapped.                                

Robert Gascoyne-Cecil, 3rd Marquess of SalisburyWith an army and navy that were utterly dwarfed by the British Empire, Portugal had no choice but to withdraw their claim over African land. Considered a massive breach of the original Treaty of Windsor in 1386, the ultimatum and subsequent aftermath were humiliating for Portugal. Indeed, the national embarrassment fuelled republican sentiment in the country, becoming one of the leading causes behind the republican revolution that would topple the Portuguese monarchy twenty years later. 

With Anglo-Portuguese relations soured, relations were only repaired in the late 1890s when Britain sought Portuguese support during the Boer War. Reaffirming the original Treaty of Windsor in a secret colonial declaration, Portugal pledged military support in the Boer War in exchange for British protection over her existing African colonies. With commercial and colonial interests being mutually assured by the two countries, the alliance could once again resume. [12]

In the twentieth century, the Anglo-Portuguese Alliance remained strong. During the First World War, Portugal joined the Entente, fighting on the Western Front. Along with honouring the recently reaffirmed Treaty of Windsor, German incursions in Portuguese East Africa (today Mozambique), meant direct involvement was unavoidable. 

Portuguese Cavalry training during the First World War, taken from the March 15th 1916 issue of 'The Illustrated War News'

During the Second World War Portugal remained neutral. Yet this worked to the advantage of Britain and her allies. With Portugal remaining neutral, it reduced the chances of Francoist Spain joining up with the Axis powers.[13] Indeed, the centuries-old alliance proved incredibly important at this time, one “without parallel in world history” [14] as Churchill described it during a debate in the House of Commons. Portugal was very much more closely aligned politically with Spain than Britain at this time as it was led by the de facto dictator António de Oliveira Salazar from 1932 to 1968. While remaining neutral proved a significant boon to the Allies, Portugal also aided the Allies by allowing the Azores islands to be used as military bases. These islands would later be offered to Britain again during the Falklands War (1982), serving once more as a base of military operations. 

In recent years the two countries have maintained strong relations. Both founding members of NATO, the alliance has remained robust and multifaceted. Portugal's entry into the European Union in 1986 further strengthened bilateral cooperation between the two nations, enabling greater economic integration and political coordination. Today, both countries continue to work closely on various regional and global issues, sharing a commitment to democratic values, human rights, and international security.

Cultural exchanges and educational collaboration also play a vital role in the alliance. Numerous Portuguese communities in the UK and British expatriates in Portugal contribute to the maintenance of cultural ties. Academic institutions from both nations foster educational partnerships, with accompanying student exchanges and research collaborations, enriching the intellectual landscape of both countries. The prestigious Portuguese Language Centre at King's College London and the Portuguese Cultural Centre in Manchester are examples of efforts to promote cultural understanding and appreciation.

Looking ahead, the Anglo-Portuguese Alliance is poised to thrive and adapt to contemporary challenges. “Brexit”, the UK's withdrawal from the European Union, has prompted both countries to re-evaluate their relationship and to explore new avenues for collaboration. Bilateral ties are likely to intensify in areas such as trade, security, and tourism, as both nations seek to strengthen their global standing in a changing geo-political landscape.

The oldest alliance in the world, the Anglo-Portuguese relationship has weathered many storms; surviving wars, political upheaval, and conflicting colonial agendas. From its medieval origins, the Alliance has evolved into a modern partnership that encompasses economic, defence, cultural, and educational ties. Spanning over six centuries, the alliance has proven instrumental in shaping the history of Portugal and the United Kingdom. From their joint efforts during the “Age of Exploration” to their struggle against Napoleonic forces, the alliance has demonstrated its resilience and mutual benefit. 


 [1] Prestage, Edgar. 1934.Transactions of the Royal Historical Society, Vol. 17: 69.

 [2] “History’s Unparalleled Alliance: The Anglo-Portuguese Treaty of Windsor, 9th May 1386 - History of Government.” Accessed Via:

 [3] Peter Edward Russell. 1955. The English Intervention in Spain & Portugal in the Time of Edward III & Richard II. Oxford, Clarendon: 397

 [4] Myers, A R. 2013. English Historical Documents. 4. [Late Medieval]. 1327 - 1485. Psychology Press: 4.

 [5] Prestage, Edgar. 1934.Transactions of the Royal Historical Society, Vol. 17: 89.

 [6] Chandler, David. 1995. The Campaigns of Napoleon. London: Weidenfeld & Nicolson: 588.

 [7] Esdaile, Charles. 2015. The Peninsular War. St. Martin’s Press: 87

 [8] Ibid: 577

 [9] Bethell, Leslie. Brazil: Essays on History and Politics. University of London Press, 2018. 57

 [10] 3rd Viscount Palmerston, Temple, Henry. 1848 “Remarks in the House of Commons” (Debate, House of Commons, London, 1st March 1848)

 [11] Howes, Robert. “The British Press and Opposition to Lord Salisbury’s Ultimatum of January 1890.” Portuguese Studies 23, no. 2 (2007): 154.

 [12] Wheeler, Douglas L, and Walter C Opello. 2010. Historical Dictionary of Portugal. Scarecrow Press: 280

[13] Leite, Joaquim da Costa (1998). "Neutrality by Agreement: Portugal and the British Alliance in World War II". American University International Law Review. Washington College of Law. 14: 185–199.

 [14] Churchill, Winston. 1943 “Remarks in the House of Commons” (Debate, House of Commons, London, 12th October 1943)

Authored by Rex Cleaver

Rex Cleaver

Rex is an Editorial Assistant at British Online Archives

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