The modern relationship between the United States and the United Kingdom (UK) was forged during the Second World War. It was cemented during the Cold War, as both countries worked together bilaterally and within NATO to counter the threat of the Soviet Union. The United States and the UK are two of the five permanent members of the United Nations Security Council, and both are founding members of NATO. In the early 1990s, the UK was an important U.S. ally in the first Gulf War, and the two countries later worked together in stabilization and peacekeeping operations in the Balkans. The UK was the leading U.S. ally in the 2003 invasion of Iraq and subsequent stabilization operations, and it was the largest non-U.S. contributor to the NATO-led mission in Afghanistan. The UK remains an important U.S. partner in ongoing global security challenges, such as combatting international terrorism, countering the Islamic State terrorist group, and opposing Russia's annexation of Crimea and actions destabilizing Ukraine, including by supporting strong sanctions in response to these actions. The UK is also the sixth-largest economy in the world and a major financial center. The United States and the UK share an extensive and mutually beneficial trade and economic relationship, and each is the other's largest foreign investor. U.S. and UK officials, from the Cabinet level down, consult frequently and extensively on many global issues. American and British diplomats report often turning to each other first when seeking to build support for their respective positions in multilateral institutions or during times of crisis, as in the immediate aftermath of the 9/11 attacks on the United States. British input is often cited as an element in shaping U.S. foreign policy debates. Some observers assert that a common language and cultural similarities, as well as the habits of cooperation that have developed over the years, contribute to the ease with which U.S. and UK policymakers interact with each other. The term special relationship has often been used to describe the high degree of mutual trust between the two countries in cooperating on diplomatic and political issues. The special relationship also encompasses close intelligence-sharing arrangements and unique cooperation in nuclear and defense matters. The government of the UK is led by Prime Minister Theresa May of the Conservative Party. She became prime minister in July 2016, after David Cameron resigned in the wake of leading the unsuccessful campaign for the UK to remain in the European Union (EU). Cameron's departure came after having been reelected in May 2015 with an absolute majority for the Conservatives. As the longest-serving home secretary in modern times, May oversaw the UK's counterterrorism, policing, crime, and immigration policies from 2010 to 2016. A Member of Parliament (MP) since 1997, she is the UK's second female prime minister. May remained prime minister after the UK election of June 8, 2017, resulted in a hung parliament, an outcome in which no single party won a majority of seats in the 650-seat House of Commons. With 318 seats, the Conservative Party came in first place but lost the majority it had after winning 331 seats in the 2015 election. The Labour Party came in second place, outperforming most expectations by winning 262 seats, a gain of 30. This result was not what Prime Minister May had in mind in April 2017 when she reversed her earlier assertions and unexpectedly announced a snap election shortly after opening the two-year window for negotiating the UK's exit from the EU (commonly termed Brexit ). At that time, polls showed a 20-point Conservative lead over the Labour Party, and May expected both to solidify her political mandate for the negotiations with an expanded majority and gain two years in the electoral calendar in which to manage the withdrawal process (by pushing the next general election back from 2020 to 2022). Polls showed the lead shrinking as the vote neared, however. Prime Minister May sought to portray her leadership as the only choice for preserving stability and delivering Brexit, but some observers criticized her campaign as dull and uninspiring. Many observers also interpreted the result as a reflection of voter unease about Brexit and the government's approach to the negotiations, pointing especially to higher turnout among young voters (who largely oppose Brexit). The Labour Party was relatively effective in focusing on concerns about proposed Conservative social and economic policies, to the extent that some voters seemingly overcame previous doubts about Labour Party leader Jeremy Corbyn, often derided as radically left-wing. Prime Minister May was able to form a Conservative minority government after concluding a deal for support from the Democratic Unionist Party (DUP), the largest unionist political party in Northern Ireland, which holds 10 seats in Parliament. The arrangement is not a formal coalition but rather a "confidence and supply" arrangement that allows the DUP certain concessions in return for its support in passing the budget and backing the government in any no-confidence votes. Legislation typically is supported on a case-by-case basis, potentially granting the DUP a pivotal role in determining the fate of certain bills. The DUP is one of the UK's most socially conservative parties, and it campaigned strongly in favor of Brexit. (Nearly 56% of voters in Northern Ireland supported remaining in the EU.) Since 2007, the DUP has led Northern Ireland's devolved regional government in a power-sharing arrangement with Irish nationalist party Sinn Fein, and it remains engaged with Sinn Fein in talks to reestablish the devolved government following regional elections in March 2017. The Conservatives granted the DUP more budgetary resources for Northern Ireland as a key part of the two parties' parliamentary support deal, and the DUP remains a significant factor in Brexit negotiations related to Northern Ireland. Other notable outcomes from the June 2017 election included the following: After gaining 50 seats in the 2015 election, the Scottish National Party (SNP) suffered the loss of 21 seats. The result dealt a blow to the aspirations of some SNP leaders for a second vote on Scottish independence following the 2014 referendum, which favored staying in the UK. After positioning themselves as the most pro-Remain party in the Brexit debate, the Liberal Democrats made modest gains, from 8 seats to 12. The Conservatives' losses occurred despite making inroads in Scotland and gaining vote share from the collapse of the populist, anti-EU UK Independence Party (UKIP). Labour also benefitted from an unexpected return of UKIP voters in some parts of England. Nearly 52% of British voters in the June 2016 referendum on EU membership answered that the UK should leave the EU. Factors such as economic dissatisfaction, unease with globalization and immigration, and antielite or antiestablishment sentiments played key roles in the referendum outcome. The vote was the culmination of a decades-long debate in the UK about the country's EU membership, however. Fearing a loss of national sovereignty and influence, the UK stood aside in the 1950s when the six founding countries (Belgium, France, Italy, Luxembourg, Netherlands, and West Germany) launched the first steps of European integration. The UK joined the precursor of the modern-day EU in 1973, largely to derive the economic benefits of membership but also to have a political voice on the inside as integration took shape. Nevertheless, historically many British leaders and citizens (perhaps most notably including former Prime Minister Margaret Thatcher) have been skeptical about the EU, and the relationship between London and Brussels often has been marked by ambivalence. The UK "opted out" of several major elements of European integration, such as the euro currency and the passport-free Schengen Area. British "euro-skeptics" have frequently expressed frustration that the EU tends to focus too much on internal treaties and process rather than taking a pragmatic approach to priorities such as boosting economic competitiveness, promoting a common energy policy, or improving European defense capabilities. Overall, Brexit remains the predominant issue in UK politics, and withdrawal negotiations with the EU are set to remain the UK government's top concern. With the clock ticking on a presumed exit in March 2019, Prime Minister May has sought to manage an intense debate about what Brexit should look like, pitting a desire for continued market access and free trade with the EU against demands to sharply curtail inward migration and the EU's ability to affect decisionmaking in the UK. The strategy put forth by the government in February 2017 opted for a "hard Brexit," meaning a full departure from the EU single market and customs union, and a full restoration of British sovereignty over lawmaking, including with regard to controlling immigration. The strategy indicated that the UK would attempt to negotiate a free trade agreement with the EU to secure as much access to the EU market as possible. Emboldened by the result of the June 2017 election, however, advocates of a "soft Brexit" strategy have continued to urge that the UK retain at least some elements of membership in the EU single market and agree to a multiyear transition period to smooth out shock effects from the withdrawal. Divisions over these differing viewpoints toward Brexit run through Parliament and the British public, but also through the Conservative Party and Prime Minister May's Cabinet. The "divergers," led by Foreign Secretary Boris Johnson, Environment Secretary Michael Gove, "Brexit Secretary" David Davis, and Secretary for International Trade Liam Fox, and numbering many Conservative MPs, continue to push for the government to deliver a hard Brexit. The "aligners," led by Chancellor Philip Hammond and Home Secretary Amber Rudd and comprising pro-EU MPs, continue to argue for maintaining closer ties with the EU. With her leadership weakened after the June 2017 election, many observers question how Prime Minister May can deliver a Brexit deal that satisfies both viewpoints. The tasks of managing Brexit-related tensions and disagreements within her own party, heading off rebellions from one side or the other, and finding potential areas of compromise are likely to be central challenges for the prime minister in 2018.