In the History of Martial Arts, Pankration is believed to be the earliest form of a documented complete Hand to Hand Combat style with a recorded history of at least 3000 years.
It started in ancient Greece and is thought to be the first "all encomposing" (both Grappling and Striking) Martial Art. Although some Martial Arts historians believe Martial Arts in China and India developed around the same time, they weren't known to the outside world.
And since Kung Fu or Wushu as its known in China did not become well known until the sixth century, several hundred years after Alexander The Great's army had brought Pankration to India, it makes sense that Pankration may have been first.
This theory is that the history of Martial Arts started in ancient Greece and spread to India when Alexander The Great invaded India in 327 B.C. His soldiers who were trained in Pankration taught the people in India that Fighting Art. And from there it spread south throughout the Indian sub-continent and north to China. Possibly being mixed with fighting styles already in that region.
Another theory is that Hand to Hand Combat arts started in various regions at roughly the same time because people from different parts of the world were experiencing the same problems.
(Being attacked by enemies, or someone trying to kill you) back then they couldn't dial 911. So they needed to know how to defend themselves. The world was a rough place in ancient times, and knowing how to fight could add years to your life expectancy.
Throughout the History of Martial Arts some Hand to Hand Combat systems were more advanced than others, and some more complete than others. Containing both Striking and Grappling, as opposed to only Striking or only Grappling.
Most if not all borrowed techniques from other styles. These ancient people had a lot of knowledge of the body, how it worked and how to inflict damage to it.
As Martial Arts evolved, one type of Fighting Art may have become more popular than another because a Famous Fighter was trained in that art or because a King favored a certain style and influenced his people to train in that art.
Whatever the reasons, some styles of Hand to Hand Combat have survived and are thousands of years old, and some have been lost to Martial Arts history.