Operating as the most feared warriors in Japan, Samurai practiced Zen Buddhism, and used it to bring a fearless and ruthless attitude to battle from 700 all the way through the 1800s. Wielding Katanas and sporting unique armor, there’s a reason Samurai are some of the most referenced warrior groups in history.

The Vikings took pleasure in pillaging and plundering all around Europe and Scandinavia during the turn of the first millennium, using their aggressive tactics and mastery of the sea. The Viking warrior culture was strong, and entry into the afterlife, Valhalla, could only be achieved through death in battle. Some historians believe they made it all the way to the new world.

There are few, if any, modern training regimens more difficult than that of the Danish Frogman Corps. Every year, over 500 applicants are whittled down to around a dozen, and since the program’s inception in 1957, there have only been around 350 accepted. They specialize in anti-piracy, anti-terrorizm, and other water-based operations.

The battle-ready Greek city-state hand picked boys at birth, and trained them in a warrior culture until they were ready. From 650 to 200 AD, there was no more effective military force, and the Spartans lived and breathed the warrior lifestyle, earning their feared place in history.

Perhaps the most effective fighting force in history, under the direction of Ghengis Kahn, the Mongol Horde conquered the largest contiguous land empire in history. Using fast moving horses and bows and arrows, they had no contemporary rivals and went largely unbeaten. The Great Wall of China was constructed in response to their power.

The Zulu were an African people that ruled the Mthethwa Empire during the mid 1800s. They used their strong military force to consolidate previously independent areas, and specialized in fast-moving tactics, and combat with spears and shields. When the British arrived in Africa in the late 1800s, they had a difficult time penetrating Zulu-controlled regions. The Anglo-Zulu War was a violent affair, in which the Zulu almost repelled a vastly technologically superior force.

Predating the Mongolian empire by a few hundred years, the Huns were incredibly talented riders and archers themselves. Although mostly nomadic tribes, under Attila the Hun they amassed the large, but short-lived Hunnic Empire.

Without the fearsome Roman military, the Roman empire would never have become the historical powerhouse that it was. Fierce loyalty, advanced tactics, and recognizable armor meant that spear and shield-wielding Roman forces dominated battlefields for centuries.

During the colonial era, there was no force more prevalent than the British Redcoats. Operating with the help of the dominant Royal Navy, the Redcoats put their discipline and technological advantages to effective use around the world.

Created in 1977, Delta Force is the most highly specialized group within the United States military, (that we are aware of). Coupling the most advanced military technology in history with modern optimized training, they are quite possibly the most deadly combat unit in history.