One year preparation
For exactly one year, the Black Beast had disappeared. In this short time frame, humanity was able to recuperate and made and gathered many weapons for when the Beast would appear again. Eventually, the Six Heroes appeared and the situation took a turn. Konoe A. Mercury of the Six Heroes passed her knowledge of sorcery, the mystic force of the universe, to mankind. Unfortunately, sorcery could not be used in its basest form by humans, as they were unable to manipulate and control it. Humans did a great deal of research into the subject and eventually developed something known as Magic Formula.
End of the Great Dark War
After one year of inactivity, the Black Beast resurfaced. Unfortunately, Magic Formula alone was not enough to defeat the Beast, so mankind created something more powerful, called Magic Formula Armament, which could be used to directly combat the Beast. After the humans figured out how to use Magic Formula and Magic Formula Weapons, they fought alongside the Six Heroes; the Black Beast was finally defeated in January 1, 2110.