President Donald Trump made headlines on Wednesday for his criticism of allies in the North Atlantic Treaty Organization (NATO) during a summit in Brussels.
The president has criticized member states for not paying enough for the protections they receive from the U.S. as a part of the organization. He added that all nations must increase their contributions from 2 percent of their gross domestic product to 4 percent.
Trump also criticized Germany on Wednesday, saying the European nation is "totally controlled" by Russia and is becoming a "captive," citing an oil deal between Berlin and Moscow
To better understand NATO, here's a closer look at the organization—including its leaders and member countries.
President Donald Trump reaches out to British Prime Minister Theresa May at the 2018 NATO Summit on July 11, 2018, in Brussels.Jasper Juinen/Getty Images
What countries are part of NATO?
Twelve nations founded NATO in 1949: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, Netherlands, Norway, Portugal, United Kingdom and the United States. The alliance has since grown to 29 members, with Montenegro being the most recent to join in 2017.
Who heads NATO?
NATO Secretary General Jens Stoltenberg speaks to reporters at the 2018 NATO Summit at NATO headquarters on July 11, 2018 in Brussels, Belgium Sean Gallup/Getty Images
NATO Secretary-General Jen Stoltenberg, a national of Norway, has led the international alliance since October 2014. He previously served as the prime minister of his country from 2005 to 2013.
Who are NATO's international leaders?
U.S.
U.S. President Donald Trump speaks to reporters on the South Lawn before boarding Marine One and departing the White House, on July 9, 2018 in Washington, DCAl Drago/Getty Images
President since January 2017, Donald Trump serves as the head of state and head of government, making him the top national leader to represent the U.S. in the NATO alliance.
Former Sen. Kay Bailey Hutchison (R-TX) testifies during her confirmation hearing to be United States permanent representative on the Council of the North Atlantic Treaty Organization, during a Senate Foreign Relations Committee hearing on Capitol Hill, June 20, 2017 in Washington, DCMark Wilson/Getty Images
Kay Bailey Hutchison, a former Republican senator from Texas, became the U.S. ambassador to NATO in August 2017. Speaking to reporters at the summit, Hutchison said, "The major thing, the major deliverable, the major overall theme of this summit is going to be NATO's strength and unity."
United Kingdom
German chancellor Angela Merkel, Prime Minister Theresa May and Polish Prime Minister Mateusz Morawiecki attend a press conference during the second day of Western Balkans summit at Lancaster House on July 10, 2018 in London, EnglandStefan Rousseau - WPA Pool/Getty Images
British Prime Minister Theresa May took office in July 2016. Although the Queen of England is technically the head of state for the United Kingdom, the prime minister leads political and state affairs, including relations with NATO. Taking aim at recent resignations that racked May's government this week, Trump said on Tuesday that the U.K. is "in somewhat turmoil," suggesting a planned meeting with Russian President Vladimir Putin will be his easiest during his Europe trip.
Germany
German Chancellor Angela Merkel (CDU) arrives for the weekly cabinet meeting in the German Chancellory on July 11, 2018 in Berlin, Germany Michele Tantussi/Getty Images
Chancellor Angela Merkel has led Germany since she rose to power in 2005. Merkel defended her country against Trump's criticism on Wednesday, "I have experienced myself how a part of Germany was controlled by the Soviet Union. I am very happy that today we are united in freedom ... because of that we can say that we can make our independent policies and make independent decisions," she said.
France
French President Emmanuel Macron holds a press conference on the final day of the European Council leaders' summit on June 29, 2018 in Brussels, BelgiumJack Taylor/Getty Images
Emmanuel Macron became president of France in May 2017. Tensions between France and the U.S. have increased significantly in recent weeks, as Trump's trade war has escalated. At the Group of Seven (G-7) summit in Canada last month, Macron said France and the other wealthy nations would be just fine without support from the U.S.
Canada
Canadian Prime Minister Justin Trudeau (L) and Canadian Defense Minister Harjit Sajjan arrive at the 2018 NATO Summit at NATO headquarters on July 11, 2018 in Brussels, BelgiumSean Gallup/Getty Images
Justin Trudeau has led his country since he became prime minister in 2015. At the summit, Trudeau has defied Trump's demands to increase military spending, moving instead to decrease funding.
Turkey
U.S. President Donald Trump (L) and Turkish President Recep Tayyip Erdogan attend the opening ceremony at the 2018 NATO Summit at NATO headquarters on July 11, 2018 in Brussels, BelgiumSean Gallup/Getty Images
President Recep Tayyip Erdoğan has led Turkey as president since 2014. Prior to that, he served as prime minister of the country from 2003 to 2014. He recently won re-election, at which time he gained sweeping new powers that came after constitutional changes made during his previous term.
Norway
Norway's Prime Minister Erna Solberg (L) shakes hands with NATO Secretary General Jens Stoltenberg (R) during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018DENIS CHARLET/AFP/Getty Images
Erna Solberg assumed office as Norway's prime minister in 2013. Her country has seen increased tensions with Russia in recent months, as her administration has asked the U.S. to significantly increase the number of troops it stations in the country. Russia sees the move as a provocation, due to its proximity to Norway.
Poland
Poland President Andrzej Duda (L) shakes hands with NATO Secretary General Jens Stoltenberg (R) during the NATO (North Atlantic Treaty Organization) summit, at the NATO headquarters in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Polish President Andrzej Duda has held office since 2015. His right-wing government has drawn criticism from other European leaders. At the same time, Poland has increasing concerns about Russia's expansionist ambitions and has reportedly offered $2 billion for the U.S. to be stationed permanently within its borders.
Belgium
Belgian Prime Minister Charles Michel (L) is welcomed by NATO Secretary General Jens Stoltenberg (R) as he arrives for the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018.ERIC LALMAND/AFP/Getty Images
Charles Michel has been the prime minister of Belgium since 2014. Belgium hosted the NATO summit at the organization's headquarters in Brussels.
Albania
Prime Minister of Albania Edi Rama (L) shakes hands with NATO Secretary General Jens Stoltenberg (R) during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Edi Rama has been the prime minister of Albania since 2013.
Bulgaria
Bulgaria President Rumen Radev (L) shakes hands with NATO Secretary General Jens Stoltenberg (R) during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Rumen Radev became president of Bulgaria in 2017.
Croatia
Croatia's President Kolinda Grabar-Kitarovic arrives to attend the NATO summit, in Brussels, on July 11, 2018 ERIC LALMAND/AFP/Getty Images
Kolinda Grabar-Kitarovic became president of Croatia in 2015.
Czech Republic
French President Emmanuel Macron (L) speaks with Czech Republic President Milos Zeman after arriving to attend the North Atlantic Council meeting during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018EMMANUEL DUNAND/AFP/Getty Images
Milos Zeman assumed office as president of his country in 2013.
Denmark
Denmark's Prime Minister Lars Lokke Rasmussen (R) arrives to attend the NATO summit, in Brussels, on July 11, 2018DENIS CHARLET/AFP/Getty Images
Lars Lokke Rasmussen took office as prime minister of Denmark in 2015.
Estonia
Estonia's Prime Minister Juri Ratas (L) shakes hands with NATO Secretary General Jens Stoltenberg (R) during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Juri Ratas took office as prime minister of Estonia in 2016.
Greece
Greece Prime Minister Alexis Tsipras (L) is welcomed by NATO Secretary General Jens Stoltenberg (R) as he arrives for the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018ERIC LALMAND/AFP/Getty Images
Alexis Tsipras assumed office as prime minister of Greece in 2015.
Hungary
Hungarian Prime Minister Viktor Orban arrives for the NATO (North Atlantic Treaty Organization) summit, at the NATO headquarters in Brussels, on July 11, 2018 FRANCOIS MORI/AFP/Getty Images
Prime Minister Viktor Orban has held the position in Hungary since 2010.
Iceland
Iceland Prime Minister Katrin Jakobsdottir (L) speaks with NATO Secretary General Jens Stoltenberg (R) during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018DENIS CHARLET/AFP/Getty Images
Katrin Jakobsdottir assumed office as prime minister of Iceland in 2017.
Italy
Italy's Prime Minister Giuseppe Conte (C) and Italy's Minister for Foreign Affairs Enzo Moavero Milanesi (R) arrive to attend the NATO summit, in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Giuseppe Conte became prime minister of Italy in June.
Latvia
Latvia's President Raimonds Vejonis speaks to journalists as he arrives to attend the NATO summit, in Brussels, on July 11, 2018DENIS CHARLET/AFP/Getty Images
Raimonds Vejonis assumed office as president in 2015.
Lithuania
Lithuania President Dalia Grybauskaite (L) is welcomed by NATO Secretary General Jens Stoltenberg (R) as she arrives for the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018 ERIC LALMAND/AFP/Getty Images
Dalia Grybauskaite has been president of Lithuania since 2009.
Luxembourg
Luxembourg's Prime Minister Xavier Bettel (C) arrives with Luxembourg's Defence Minister Etienne Schneider (L) to attend the NATO summit, in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Xavier Bettel became prime minister of Luxembourg in 2013.
Montenegro
Montenegro President Milo Dukanovic (L) arrives to attend the NATO summit in Brussels, on July 11, 2018 ERIC LALMAND/AFP/Getty Images
Milo Dukanovic took office as president of Montenegro in May.
Netherlands
Netherland's Prime Minister Mark Rutte waves as he arrives to attend the NATO summit in Brussels, on July 11, 2018 ERIC LALMAND/AFP/Getty Images
Mark Rutte has been prime minister of the Netherlands since 2010.
Portugal
Portugal's Prime Minister Antonio Costa (L) arrives to attend the NATO summit, in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Antonio Costa assumed office as prime minister of Portugal in 2015.
Romania
Romania's President Klaus Werner Iohannis answers journalists' questions as he arrives to attend the NATO summit, in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Klaus Werner Iohannis became president of Romania in 2014.
Slovak Republic
Slovak Republic's President Andrej Kiska (L) arrives to attend the NATO summit, in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Andrej Kiska has been president of the Slovak Republic since 2014.
Slovenia
Slovenia Prime Minister Miro Cerar (L) shakes hands with NATO Secretary General Jens Stoltenberg (R) during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018 DENIS CHARLET/AFP/Getty Images
Miro Cerar became his country's prime minister in 2014.
Spain
Spain's Prime Minister Pedro Sanchez (R) speaks with US President Donald Trump after arriving to attend the North Atlantic Council meeting during the NATO summit, at the NATO headquarters in Brussels, on July 11, 2018 EMMANUEL DUNAND/AFP/Getty Images
Pedro Sanchez became Spain's prime minister in June.
"We see an erosion of the global multilateral architecture, unilateral measures, unilateral sanctions becoming the norm," South Africa's envoy tells Newsweek.
