AFGHANISTAN: 12,000 to 13,000 TROOPS
At the height of the war, in 2010 and 2011, there were more than 100,000 troops in Afghanistan. When Mr Trump took office, that number was hovering around 10,000. A
new strategy, announced in August 2017, added thousands more.
Mr Trump has long bemoaned the length of the 18-year conflict, with Pentagon officials worried that, at a moment's notice, one tweet could end the mission.
The current commander, General Austin Miller, has slowly dropped troop numbers to between 12,000 and 13,000 over the past year.
American and Afghan officials, speaking on condition of anonymity to discuss details of the plan, said the eventual US force size could drop to 8,600 - roughly the initial reduction envisioned in a draft agreement with the Taliban before Mr Trump halted peace talks last month.
Rather than a formal withdrawal order, they are reducing the force through a gradual process of not replacing troops as they cycle out.
SYRIA: ABOUT 200
What started as 50 Special Operations soldiers in late 2015 ballooned to more than 2,000 in 2017 when US troops and Kurdish and Arab local fighters, known as the Syrian Democratic Forces (SDF), were battling the Islamic State of Iraq and Syria (ISIS) in Raqqa, its de facto capital.
In December 2018, before ISIS' self-proclaimed caliphate collapsed, Mr Trump issued his first of several orders to pull all US troops from the country. In turn, the Pentagon tried to shore up a plan to withdraw roughly 1,000 troops while keeping the rest spread out across the country's north-eastern corner.
In recent weeks, Mr Trump ordered those remaining troops out, leaving a small detachment of around 200 in southern Syria - at a small outpost on the Jordanian border.
Mr Trump is also said to be in favour of leaving about 200 Special Operation forces in eastern Syria to help combat ISIS guerrilla fighters and to block Syrian government forces and their Russian advisers from seizing several coveted oil fields in the east.
The other troops who left northern Syria in the past several days did not return to the United States, as Mr Trump said they would. They are now based in western Iraq.
IRAQ: ABOUT 6,000
The war that began as Operation Iraqi Freedom and lasted from 2003 to 2011 peaked at about 150,000 troops. Only a small detachment remained when US troops left altogether in 2011.
In 2014, ISIS poured over the Syria-Iraq border and routed the Iraqi army from Mosul, once the country's second-largest city, and pressed south to the outskirts of Baghdad, the capital, before being repelled.
With ISIS fighters closing on Irbil, President Barack Obama started his campaign against the terrorist group, which would come to be known as Operation Inherent Resolve. The small contingent of ground troops, helping hunt terrorist targets and advise the morale-stricken Iraqi army, grew to around 5,000 in 2016.
That number has only increased, to roughly 6,000, as US troops move from northern Syria to western Iraq.
SAUDI ARABIA AND OTHER PERSIAN GULF NATIONS: 45,000 to 65,000
In response to Iranian attacks and provocations since May, the Pentagon has deployed about 14,000 additional troops to the Persian Gulf region, including roughly 3,500 to Saudi Arabia in recent weeks. Those forces include airborne early warning aircraft, maritime patrol planes, Patriot air and missile defence batteries, B-52 bombers, a carrier strike group, armed Reaper drones and other engineering and support personnel.
But, at any given time, between 45,000 and 65,000 US troops are in the region, spread out between Jordan and Oman, assigned to operate airfields, run key headquarters, sail warships and fly warplanes, and stage for deployments to places such as Iraq and Afghanistan.
The numbers change substantially depending on the presence of an aircraft carrier strike group or two in the region, and whether a large group of Marines is afloat in those waters.
AFRICA 6,000 to 7,000
There are between 6,000 and 7,000 US troops spread across Africa, with the largest numbers concentrated in the Sahel and the Horn of Africa. In Somalia, there are about 500 Special Operations troops, fighting the Qaida-linked terrorist group, al-Shabab, from small outposts alongside local troops.
In the Sahel, in countries like Niger, Chad and Mali, there are several hundred. The Air Force recently built a large drone base, known as Air Base 201, near the city of Agadez, Niger.
Last year, Mr Jim Mattis, the defence secretary at the time, ordered the military command that oversees troops on the continent, known as Africom, to shrink its forces by several hundred Special Operations troops as part of the Pentagon's strategy to focus more on threats from Russian and China around the world.
The current commander of Africom, Gen Stephen Townsend, is completing a sweeping review that will probably mean the reduction of more troops.
JAPAN AND SOUTH KOREA: About 78,000
Since the end of World War II and the Korean War, the United States has maintained a large military presence in Asia. More than 28,000 US troops are stationed in South Korea, many living with their families. The United States and South Korea have suspended major training exercises over the past year as a concession to North Korea, but the two militaries continue to carry out smaller drills.
In Japan, the Pentagon maintains about 50,000 troops at roughly two dozen bases across the country. About 25,000 of those troops are stationed on Okinawa. Violence committed by US service members or related personnel on the island has long caused friction between Washington and Tokyo.
NATO NATIONS: MORE THAN 35,000
The Cold War put as many as 300,000 US troops across Europe to defend against the Soviet Union. That presence eventually plummeted to about 30,000 soldiers after the collapse of communism in Eastern Europe.
Over the past year, the United States and its allies in the North Atlantic Treaty Organisation (Nato) completed positioning about 4,500 additional soldiers in the three Baltic States and Poland, and they have stationed several thousand other armored troops mostly in Eastern Europe as a deterrent to Russian aggression.
Despite recent tensions with Turkey over its offensive into northern Syria, the United States flies combat and support aircraft from Incirlik Air Base in Turkey. The Pentagon also stores about 50 tactical nuclear weapons at Incirlik.
ELSEWHERE: More than 2,000
The Pentagon has deployed troops to other locations around the world. There are about 250 troops, mostly Special Forces, in the Philippines in part to help with counterterrorism operations. In the past six years, about 2,000 Marines have regularly deployed to northern Australia to act as a response force for the Pacific region.
In Japan, the Pentagon maintains about 50,000 troops at roughly two dozen bases across the country. About 25,000 of those troops are stationed on Okinawa. Violence committed by US service members or related personnel on the island has long caused friction between Washington and Tokyo.
NATO NATIONS: MORE THAN 35,000
The Cold War put as many as 300,000 US troops across Europe to defend against the Soviet Union. That presence eventually plummeted to about 30,000 soldiers after the collapse of communism in Eastern Europe.
Over the past year, the United States and its allies in the North Atlantic Treaty Organisation (Nato) completed positioning about 4,500 additional soldiers in the three Baltic States and Poland, and they have stationed several thousand other armored troops mostly in Eastern Europe as a deterrent to Russian aggression.
Despite recent tensions with Turkey over its offensive into northern Syria, the United States flies combat and support aircraft from Incirlik Air Base in Turkey. The Pentagon also stores about 50 tactical nuclear weapons at Incirlik.
ELSEWHERE: More than 2,000
The Pentagon has deployed troops to other locations around the world. There are about 250 troops, mostly Special Forces, in the Philippines in part to help with counterterrorism operations. In the past six years, about 2,000 Marines have regularly deployed to northern Australia to act as a response force for the Pacific region.