The United States and the United Kingdom share many cultural and historic ties, but they also enjoy an extraordinary set of diplomatic relations that have come to be known as the ‘Special Relationship’. The term refers to the unusually close relationship between the U.S. and the UK on political, economic, military, and diplomatic matters and has been unofficially recognized since the 19th century.

Relations between the two nations were not always strong, however. Anglo-American tensions were often strained throughout the 19th and early 20th centuries, in stark contrast to what is seen today. Great Britain was dangerously close to supporting the Confederacy in the Civil War, and the American refusal to join the League of Nations was seen as a ‘betrayal’ by the British. However, circumstances changed by World War II as the nations became closer following the fall of France in 1940 and by the leadership of Winston Churchill during his tenure as prime minister. Churchill is often credited for coining the term ‘special relationship’ during a speech in 1946, and is viewed as the father of the modern relationship. He believed in the common ties between all English-speaking countries, and he came to favor American relations over the historically strong French ties. Churchill and President Roosevelt would even exchange over 1700 letters during the course of the war.

Today, the Special Relationship has grown to encompass various policy areas. The two nations collaborate militarily through intelligence sharing agreements, shared military bases, and weapons procurement. The countries also boast close economic ties: the United Kingdom is the largest source of foreign direct investment (FDI) in the United States, and the U.S. is the largest source of FDI in the United Kingdom. Relations between the leaders of the two nations have been largely constructive as well, most famously illustrated by the strong friendship between President Ronald Reagan and Prime Minister Margaret Thatcher. However, relations between the U.S. and UK’s respective leaders have not always been on good terms. President Bill Clinton clashed with Prime Minister John Major over the crisis in Bosnia and Clinton’s decision to grant a visa to Sinn Féin leader Gerry Adam, an ardent Irish republican allegedly linked to the IRA, caused Major to ignore Clinton’s phone calls for days. Prime Minister Tony Blair’s decision to support President George W. Bush and the Iraq War won him praise in the U.S. but cost him dearly at home, lowering his approval rating to 39% and ultimately compromising his political career. President Barack Obama weighed in on the Brexit referendum during his trip to the UK in April 2016, stating that the UK would be at the ‘back of the queue’ in any potential trade deal with the U.S. if it voted to leave the European Union. These comments enraged British MPs who were campaigning for Brexit, with former UKIP leader Nigel Farage saying Obama acted ‘disgracefully’ and caused the UK to vote leave.

The Special Relationship has taken on new importance during the Trump presidency. Prime Minister Theresa May and the British government quickly sought to establish good relations with the Trump administration, and May was the first world leader to visit President Trump after his election in late January. Meanwhile, President Trump has proved to be a polarizing figure across the pond in Great Britain. In fact, an official petition to Parliament to prevent President Trump from visiting the UK reached over 1 million signatures, and a formal state visit to the UK in June was postponed amid fears that it could be disrupted by mass protests. Prime Minister May has been criticized by the British public for her relationship with the President thus far, and was even accused of being a “European mole” for Trump after leaked documents revealed that the UK had attempted to water down EU policies tackling climate change, possibly pandering to President Trump’s climate change agenda, or lack thereof.

Though controversial, the relationship between May and Trump has proved that the Special Relationship is alive and well, albeit with a conservative bent. The two leaders used May’s visit to voice their commitments to a new U.S.-UK trade deal that must be drawn up in the wake of Brexit. President Trump stated that the two nations would work quickly to implement a deal once the UK leaves the EU and assured that the UK would be at the ‘front of the line’ for trade talks in the future, a direct contrast to President Obama’s ‘back of the queue’ remarks. Despite this vote of confidence, any potential deal will be on hold for quite some time. The two countries cannot begin negotiations until the UK has left the EU, which will not happen until 2019, and it could take years to lead to an agreement. Given its cyclical nature and historical importance, however, the Special Relationship will likely endure these difficulties and continue to be an example of cooperative diplomatic relations for years to come.