© Getty Images/Reuters

History of mercenaries -

Mercenaries are as old as war itself. While there is evidence that the earliest civilizations in the world imposed a sort of draft and had standing armies, there is just as much evidence that nomadic tribes and individuals would frequently be hired to strengthen a given civilization's military.

© Public Domain

Killers for hire -

While the mercenary was once a universally accepted participant of war, different from a soldier only in respect to their loyalties and compensations, the consensus has changed, as has the job itself. In modern times, mercenaries and the private armies that employ them are associated with wartime atrocities, shadowy covert operations, and corporate warfare and oppression.

© Getty Images

The Apiru -

One of the earliest organized mercenary groups that has been discovered is the Apiru, a group of people documented in Egyptian and Sumerian texts dating back to the 2nd millennium BCE and described as wanderers offering their military services to the highest bidder.

© Public Domain

The Apiru -

The Apiru were united by occupation alone. From what historians can gather, there was no common ethnicity or even language amongst the Apiru, but they lived together on the outskirts of society, living out their days as feared, hated, but nevertheless useful mercenaries.

© Getty Images

The Ten Thousand -

As is the case with many modern private armies, the mercenaries that made up the Mighty Ten Thousand were mostly disillusioned, in this case Greek veterans of the Peloponnesian War of the 5th century BCE.

© Getty Images

The Ten Thousand -

In a story of the Ten Thousand as told by Greek military commander and historian Xenophon, after successfully defeating the Persian army in the Battle of Cunaxa, near Babylon, the mercenaries learned to their dismay that Cyrus the Younger, their employer, had died in battle, leaving them with no one to pay their bill. After unsuccessfully trying to strike a new deal with the Persians they had just defeated, the Ten Thousand were forced to retreat back to the Black Sea, an expedition that took them nine months.

© Public Domain

The Varangian Guard -

The Varangian Guard was a multiethnic group of hired swords employed by the Byzantine Empire for nearly 400 years between the 10th and 14th centuries. Mostly warriors from Slavic and Nordic nations, as well as the Rus' of modern-day Ukraine, filled out the ranks of the Varangian Guard.

© Getty Images

The Varangian Guard -

The loyalty of the Varangian Guard was bought with the highest wages of any Byzantine military unit, and they proved themselves worth the price. These trusted mercenaries turned the tide of numerous wars and battles, conflicts the Byzantines might very well have lost without the help of the Guard.

© Getty Images

The Knights Templar -

The Knights Templar were arguably one of the largest mercenary armies in history. They were so big, in fact, that they only employed themselves. Although loyal to no nation and including members from all across Europe, the Knights Templar fought in the name of Christianity, were sworn to poverty, and yet still managed to make unholy amounts of money off of their mission.

© Getty Images

The Knights Templar -

The Knights Templar fought all across Europe and the Levant, protecting Christian pilgrims and others they deemed worthy of protection. For their deeds, peasants and kings alike left gold, land, and more to the Templar Order. At one point, the Knights Templar owned the entire island of Cyprus, over a thousand castles, and enough gold to warrant opening what is considered the world's first international bank.

© Getty Images

The White Company -

One of the most infamous mercenary groups of the Middle Ages was the White Company, whose lack of loyalty allowed them to always come out on top during the myriad of conflicts of the deeply fractured Italian Peninsula of the 14th century.

© Public Domain

The White Company -

Led by Englishman John Hawkwood, the White Company consisted of thousands of mercenaries, and were so feared and influential that Italian states would often pay them immense sums of money to stay out of their conflicts altogether.

© Getty Images

The Swiss Guard -

One of the most enduring private armies in history, and also one of the most loyal, is undoubtedly the Swiss Guard, the unofficial army of the Vatican. They weren't always the Pope's personal guardsmen, though.

© Public Domain

The Swiss Guard -

During the Middle Ages, before Switzerland was the immensely wealthy country it is today, it was in fact a very poor country, and life as a sellsword was attractive to many Swiss. The Swiss Guard earned themselves a reputation as one of Europe's most elite fighting units during the French Revolution and the Napoleonic Wars. Impressed by their prowess, it was Pope Julius II who first established the Pontifical Swiss Guard.

© Getty Images

The Catalan Grand Company -

Another mercenary group made up of hardened veterans was the Catalan Grand Company, which first appeared in 1309. These mercenaries were also some of the rowdiest groups of fighters in medieval history.

© Public Domain

The Catalan Grand Company -

The group of Catalonians was first employed by the Byzantine Empire to fight off the invading Turkish forces, which they did with ease. However, they were ambushed and decimated by another group of mercenaries shortly afterward. Instead of fizzling out entirely, the surviving members first tried to establish their own state in Gallipoli, found employment under the Greeks, went to war with the Greeks promptly afterward, and won. For almost a century, the Catalan Grand Company ruled over a substantial portion of Greece before being wiped out by the Florentines.

© Getty Images

The Gothic mercenaries -

The bane of the Roman Empire for almost all of its nearly-1,000 year history were the Germanic barbarians that continuously pushed the Empire's northern borders. Sometimes, however, these Goths were employed as mercenaries by Rome, and Rome's enemies as well.

© Public Domain

The Gothic mercenaries -

Before long, there were countless Gothic mercenary regiments dotting the Roman frontier. Eventually, in 410 CE, these mercenaries banded together and descended upon the city of Rome, destroying the Empire's capital.

© Getty Images

Blackwater Worldwide -

In modern times, the private army with the most publicity is most likely Academi, formerly known as Blackwater. Based in Herndon, Virginia, Blackwater operates some of the most advanced military training facilities in the world and outsources its personnel to conflicts around the globe.

© Getty Images

Blackwater Worldwide -

Blackwater came under widespread scrutiny after the Nisour Square massacre of 2007, in which several Blackwater employees indiscriminately opened fire in a traffic circle in Baghdad, Iraq, murdering 17 civilians. Even after this incident, Blackwater didn't lose its contract with the US government.

© Getty Images

Triple Canopy -

In 2012, Triple Canopy had almost 2,000 employees in active combat in Afghanistan, after they signed a US$1.5 billion contract with the US military.

© Public Domain

Triple Canopy -

While Triple Canopy's headquarters are in the US, most of their training takes place overseas, namely in Uganda and Peru. Triple Canopy employs more than 3,000 mercenaries worldwide.

© Getty Images

Aegis Defense Services -

Aegis Defense Services, one of the largest private military companies in the world, has held a significant presence in the Middle East as well as certain countries in Africa for decades.

© Getty Images

Aegis Defense Services -

It is well known that private militaries often act with little-to-no supervision. For Aegis, the consequences of this came to national attention in 2005 when a series of 'trophy videos' were released, showing Aegis employees firing indiscriminately at civilians in Iraq out of an armored vehicle. Even after an internal investigation, the events were deemed legal due to the lax protocols applied to private defense contractors.

© Getty Images

G4S Secure Solutions -

G4S Secure Solutions might not sound familiar, but they are in fact the largest private defense company in the world. As of 2014, they were the second largest publicly traded employer in the world, second only to Walmart.

© Getty Images

G4S Secure Solutions -

G4S employs more than 600,000 mercenaries, who have been involved in numerous human rights violations, including the facilitation of illegal prison labor in Britain and the abuse of children in youth detention centers in Israel and elsewhere.

© Getty Images

G4S Secure Solutions -

The cruelty of G4S is accompanied, and complemented by, its lax employee screening which has been frequently criticized. Omar Mateen, the man who carried out the massacre at Orlando's Pulse nightclub in 2016, the second most lethal mass shooting in the history of the United States, was an employee of G4S. The company claims Mateen was screened twice with no red flags.

© Public Domain

Executive Outcomes -

Africa's most well-known and notorious private military company, Executive Outcomes, was formed in 1989 in South Africa when apartheid was diminishing and soldiers of the South African military were consequently being laid off in droves.

© Getty Images

Executive Outcomes -

Since then, Executive Outcomes, or EO, has been involved in numerous civil wars across the African continent, and have been hired to suppress corporate uprisings on a regular basis. Numerous mines of diamonds and other precious metals are supervised under the Executive Outcomes mercenary militias.

Sources: (Thought Catalog) (Insider) (Mic)

See also: The world's top 30 military powers today

© Getty Images