A US soldier.(Chip Somodevilla/Getty Images)
The United States regularly has the world's highest military expenditure, and upped its budget to $603 billion (£467 billion) this year.
But when military spend is looked at as a percentage of a country's gross domestic product (GDP), the picture is different.
This measurement looks at the relative size of a country's military spending, rather than comparing budgets.
Keep scrolling for the top 12 countries, according to the CIA Factbook's 2015 figures.
12. Jordan — 4.31% of GDP
A Jordanian soldier carries a Syrian refugee child to help him board a Jordanian army vehicle
Population: 8.2 million (97th in the world)
Jordanians must be 17 to join the military, and conscription for men was reintroduced in 2007.
In 2014 Jordan's national airline introduced new restrictions on travel for men of military age, in preparation for military action against Islamic jihadists in Iraq and Syria. The biggest age group in the country is 0-14, and the median age is 22.3.
In June, Germany announced it would move its military forces from Turkey to Jordan following a diplomatic dispute.
Jordan is a close military ally of the US and holds a strategically important position between Iraq and Syria.
11. Bahrain ---4.59%
11. Bahrain — 4.59% (Flickr/Chris Price)
Population: 1.4 million (156th in the world)
The minimum legal age for military service is 18, although non-commissioned officers, technicians and cadets can be 15. There is no conscrition.
In April Bahrain approved the use of military courts to try civilians, although officials said this would only be used for those accused of acts of terrorism. This was last enforced during a three month state of emergency in 2011 when the government suppressed mass pro-democracy protests. The country has stripped dissenters of their citizenship, according to the Washington Post.
Long standing tensions exist in the country between the Shia majority and Sunni population, and the country is ruled by a Sunni king.
10. Lebanon — 4.76% of GDP
Hundreds of Syrian families wait to register at the United Nations High Commissioner for Refugees headquarters in Beirut, Lebanon, on Jan. 30, 2017.(AP/ Hassan Ammar)
Population: 6.2 million (108th in the world)
The legal minimum age for voluntary military service is between 17 and 30, and there is no conscription.
Parts of Lebanon are still controlled by Hezbollah — a Shi'a Islamist military group and political party, named as a terrorist organisation by the European Union. Hezbollah was involved in a war with Israel in 2006.
Meanwhile, in 2012 the Syrian conflict spilled into Lebanon, and tensions and violence in the country escalated. According to the UN refugee agency, there are now over one million Syrian refugees in Lebanon.
9. Namibia — 4.82%
Namibia's President Hage Geingob receives guard of honour upon arrival at the airport in Abuja, Nigeria May 28, 2015.
Population: 2.4 million (143rd in the world)
More than a third of Namibia's population is 14 or under, and the median age is 21. There is no conscription, and citizens can sign up for voluntary military service from the age of 18.
Although Namibia spends a relatively high proportion of its GDP on its military, this is more reflective of its small GDP than indicative of military might. The country is politically stable, although suffers from extreme social and economic inequalities. Namibia experienced a period of economic growth between 2011 and 2015, although sufficient job creation remains a problem.
8. Russia — 5.01% of GDP
In 2014, Russian troops invaded Crimea.(Dan Kitwood / Getty)
Population: 142.4 million (10th in the world)
Men in Russia must register for military service at the age of 17, and must do a minimum of one year's service between the ages of 18 and 27.
Russia is currently embroiled in the Syria conflict, on the side of the Syrian government, although this has drawn strong criticism. On Friday President Vladimir Putin agreed a ceasefire with US President Donald Trump in southwest Syria in an effort to stem the civil war.
In 2014 Russia annexed the Republic of Crimea, officially a region of the Ukraine, which caused an international outcry.
Last week, the chairman of NATO's Military Committee told Politico that Russia was advancing its nuclear and ballistics capabilities, but could not say why.
7. Israel — 5.38% of GDP
Two Israeli Border Police officers detain Palestinian photographer Shadi Hatem, during a protest organized by activists in support of Palestinian prisoners in the Israeli jails, in front of the Israeli Offer prison, near the West Bank city of Ramallah, Wednesday, August 3, 2016.
Population: 8.2 million (99th in the world)
Both men and women must do military service, although men must serve for longer (32 months compared to women's 24 months).
Israel has been locked in a conflict over territory with neighbouring Palestine for years, despite numerous attempts by international forces to broker a peace agreement. Israelis have ruled over Palestinians in the West Bank, in the east of Israel, and eastern Jerusalem since 1967, and low-level fighting between the two sides are ongoing.
US President Donald Trump boasted before his election that he could help broker a peace deal between the two nations, but reports from June suggested he may be considering pulling out of the process.
6. Azerbaijan — 5.61% of GDP
A house which was damaged during clashes between Armenian and Azeri forces is seen in Nagorno-Karabakh region, which is controlled by separatist Armenians, in this still image taken from video provided by Nagorno-Karabakh region Defence Ministry April 2, 2016.
(REUTERS/Nagorno-Karabakh Military Handout via Reuters TV)
Population: 9.9 million (92nd in the world)
Men between 18 and 35 are required to perform military service for 18 months, or for 12 months if they are university graduates.
The landlocked region of Nagorno-Karabakh remains disputed territory between Azerbaijan and Armenia.
A ceasefire, brokered in 1994, was violated severely last year when troops marched on the region and hostilities heated up. Azerbaijan also said Armenia had broken it 128 times in 24 hours on Tuesday.
5. Algeria — 6.24% of GDP
President Abdelaziz Bouteflika. (Thomson Reuters)
Population: 40.3 million (34th in the world)
The legal age for military service is 17, and men are conscripted for 18 months between the ages of 19 and 30.
Algeria suffered a civil war beginning in 1992, sparked by a military coup against the Islamic Salvation Front. The war led to the deaths of more than 100,000 people, with thousands more missing. In 1999 President Abdelaziz Bouteflika, who still rules Algeria, agreed a peace deal with the rebels and banned the Islamic Salvation Front party.
In June, Algeria joined Egypt and Tunisia in calling for political dialogue to end the crisis in neighbouring Libya, rejecting a military solution.
4. Iraq — 7.28% of GDP
A member of the Counter Terrorism Service walks past the ruined Grand al-Nuri Mosque in the Old City in Mosul (Thomson Reuters)
Population: 38.1 million (37th in the world)
The median age in Iraq is 19.9, and military service is open to those aged between 18 and 40. There is no conscription.
Military spending in Iraq has increased considerably since 2011, when it stood at 3.18% of GDP.
Iraq was ravaged by war between 2003 and 2011, that began following an invasion by a United States-led coalition to topple Saddam Hussein. The UK's Chilcot inquiry has since condemned the war as unnecessary since Hussein did not pose an immediate threat to the UK and intelligence reports that he had weapons of mass destruction were false.
The governments that have held power in Iraq since Hussein have battled to keep order, and the country is still suffering violence and instability. In 2014, ISIS seized large parts of the country. Much of this territory has since been regained, but thousands of people have been displaced in the conflict.
3. South Sudan — 10.32% of GDP
A South Sudanese man holds a gun in his village.(Flickr/Steve Evans)
Population: 12.3 million (75th in the world)
The median age in South Sudan is 17.1, and over 44% of the population is between the age of 0 and 14. However, charity UNICEF estimates that more than 17,000 child soldiers have been used to help fight the country's civil war, which began in 2013. Despite this, 18 is the legal minimum age for both compulsory and voluntary military service.
The war erupted after President Salva Kiir accused his former vice-president of plotting a coup. Although a ceasefire was brokered in 2014, it has been repeatedly broken.
The war has caused over one million people to be displaced, and reports suggest civilians are being routinely targeted. In December 2016, the UN said ethnic cleansing was occurring in some parts of the country.
In February, the UN formally declared a famine in parts of South Sudan, warning that 100,000 people were facing starvation and over a million were on the brink of famine. In May, the President declared a ceasefire, but the violence has continued.
2. Saudi Arabia — 13.5% of GDP
Saudi youths demonstrate a stunt known as "sidewall skiing" (driving on two wheels) in the northern city of Hail, in Saudi Arabia March 30, 2013.
Population: 28.2 million (47th in the world)
The minimum legal age for men (women are not permitted) to join the military in Saudi Arabia is 17, and there is no conscription.
In May, oil-rich Saudi Arabia signed a $110 billion weapons deal with the United States, which included items that had been put on hold under the Obama administration due to concerns about civilian deaths in Saudi's attacks on Yemen.
The British government has also been criticised for continuing to sell arms to Saudi, despite civilian deaths in Yemeni raids.
Saudi and its allies in the Middle East cut diplomatic ties with and imposed sanctions on Qatar earlier in June, after accusing the country of supporting extremism. After issuing an ultimatum last week, Saudi announced on Wednesday that it had received a response, and would reply in due course.
1. Oman — 14.58% of GDP
Oman's leader Sultan Qaboos bin Said.(REUTERS/Fadi Al-Assaad)
Population: 3.4 million (134th in the world)
The legal age for voluntary military service is between 18 and 30, and there is no conscription.
The UK sold £2.5 billion worth of weapons to Oman, a close ally, in 2013, and the UK government has a military base in Oman's Duqm Port complex. But human rights campaigners have criticised the UK's support for the country: Human Rights Watch says Oman does not permit freedom of expression, discriminates against women and allows the abuse and exploitation of migrant workers.