Summary of the story
Between Guild Wars 1 and Guild Wars 2
A group of adventurers in search of glory had to unchain its fury on the Great Destroyer, a "charming creature" whose the origins remain dark.
It was my great-grandfather who led the punitive strike to shoot down the Animal, it was him the hero whose exploits we so much told during the decades which followed the death of the Great Destroyer... It is him whom today everybody curses, sad irony of fate...
But you must be a little lost. Let me summarize of the beginning.
250 years ago of it, in a period when the miracles and the tragedies were daily on the lands of Tyria, Cantha and Elona, appeared a threat of an unprecedented amplitude. 
The world, saved repeatedly, in particular the chaos caused by the deaths alive, led by Lich and later of a treacherous answering in the name of Shiro Tagachi with his army of afflicted and of shiro' ken. Then, more recently, hardly saved by the madness to conquer the world and to take back 
his rights as God, Abaddon, the famous God outcasted by five others (For reminding: Grenth, God of Death and Ice, Dwayna, Goddess of Life and Air, Balthazar, God of War and Fire, Melandru, Mother of nourishing Earth and Nature and finally Lyssa, twin Goddess of Beauty and Illusion who is the latest of the former immortal). And indeed this world, being subjected to heavy events, was again threatened by the Great Destroyer.
Well before these events, the Tome of the Rubicon had already announced its arrival, predicting an immense battle between the Great Dwarf and the Great Destroyer who would lead to the extinction of the race of the dwarfs. They were not if far from the account finally, because the dwarfs became a legend today and the rare survivors of which have to be in hiding somewhere underground. Nobody saw it for decades.
The group of hero led by my ancestor, having managed of the exploit to reunite the troops of Ascalon, Norns and Asuras to fight the enemy, arrived finally in front of the Great Destroyer. After a long and difficult fight, the Animal died. The beginning of the tranquillity? Yes, but it is not everything... The Great Destroyer was only a pawn of a vaster plot.
By destroying the monster in its lair of fire and lava, my ancestor raised the head and saw a very beautiful statue, really the ancient dragon of the name of Primordus, the first one to have woken up. It called its other congeners to wake up from their torpor millennium. Glint and Kuunavang are only larvas compared with the power of the ancient dragons.
So many events took place between this day of enjoyment and jubilation and today, where the world returns into the chaos. I am too young to have been able to follow myself the events, but the Ancients and their manuscripts contain many things about this period of the history which fascinates me. I am going you to tell main lines.
Our ancestors who lived on these lands 250 years ago would be surprised discovering the geopolitical evolutions of our dear world...