The World's Most Powerful Mercenary Armies

Its been a banner decade for modern military fighting. In 2010 alone there were more than 70 armed conflicts across the globe from Sangin to Ingushetia.

As different as each of them were, they all had one thing in common, at some point one side wanted more troops.

Most battles eventually come down to boots on the ground and rifles in the field. So when commanders are building their ranks it's often with professional soldiers who know how to fight, and get paid well to do it.

The idea of a mercenary may seem a bit quaint in the 21st century, but those forces make a difference and are often all that stands between a leader and his fate.

Security giant G4S is the second-largest private employer on earth

With more than 625,000 employees, this listed security giant is the second-largest private employer in the world (behind Wal-Mart). While some of its business is focused on routine bank, prison and airport security, G4S also plays an important role in crisis-zones right around the world.

In 2008, G4S swallowed up Armorgroup, whose 9,000-strong army of guards has protected about one third of all non-military supply convoys in Iraq (it's also notorious for its wild parties and for having Afghan warlords on its payroll).

But the combined group has a security presence in more than 125 countries, including some of the most dangerous parts of Africa and Latin America, where it offers government agencies and private companies heavily-armed security forces, land-mine clearance, military intelligence and training.

Unity Resources Group is active in the Middle East, Africa, the Americas and Asia

With more than 1,200 staff worldwide, the Australian-owned Unity Resources has been able to grow its presence in Iraq as sovereign armies withdraw. Its management consists of veterans from Australia, the U.S. and Great Britain.

The private military firm is best-known for guarding the Australian embassy in Baghdad, where, as of 2010, it had trained Chilean soldiers to man gates and machine-gun nests. Unity personnel were also responsible for two controversial car shootings in Iraq: one killed an Australian professor, another resulted in the deaths of two civilian women.

Outside Iraq, Unity has assisted with security during parliamentary elections in Lebanon and helped evacuate private oil companies from crisis zones in Bahrain. The firm also operates throughout Africa, the Americas, Central Asia and Europe.

Erinys has guarded most of Iraq's vital oil assets

Erinys has also followed U.S. State Department contracts to Iraq. Its biggest mission in recent years took 16,000 of its guards to 282 locations around the country, where they protected key oil pipelines and other energy assets.

The group also maintains a presence in Africa, where it has traditionally focused its operations. Erinys was recently awarded two contracts in the Republic of Congo, for security at major iron ore and oil and gas projects. 

Please follow Military & Defense on Twitter and Facebook.