If you don’t mind spoilers, here’s an entry from Panzer Dragoon Orta’s in-game encyclopaedia that should give you a good idea:
< The Great Fall >
A period of great change, the world was
in upheaval with the fall of the former
According to the official Imperial records,
in Imperial Year 119, the fleets of Arwen
and Zastava, led by the traitor,
K. F. Craymen, attempted a coup of
After wiping out all the satellite regions
of the Empire, Craymen and his men
activated the ruins near Lake Ul in
the northeast section of the Continent.
Consequently, a great many
bio-engineered creatures emerged from
the ruins and ran rampant, causing
further damage to the Empire’s remote
cities and regions.
It is said that the Seventh Emperor
himself, deeply affected by the death of
many of his subjects, rose to challenge
the ancient ruins by using the power of
the imperial fortress, Grig Orig.
His Majesty sacrificed his own life to
eradicate the foul creatures that resided
within the ruins, and even disabled many
of the surrounding ancient ruins with
To honor this heroic act, the present
Empire has declared an annual
"Guardian Festival" in which all subjects
of the Empire are required to fast for
the full four days and four nights of
Over the next decade following
the destruction of the ancient ruins,
the Continent’s topography and climate
began to change radically.
Cartographers had much difficulty
keeping up with the ever-changing
landscape, and maps were constantly
Floods caused by the melting of
the polar regions resulted in large areas
of land being swallowed by water,
earthquakes created vast canyons and
gave birth to new mountains,
and the difference in temperature
between the various regions of the land
grew further and further apart.
Various studies show that the total
human population of the Continent
deceased to less than half of its former
glory during this period of turbulence.
Modern historians have dubbed this era
"the Great Fall."
The immense tragedies that befell
the Empire have been engraved into
the minds of the people, and is generally
regarded as the time of greatest
turmoil that man has ever known since
the fall of the Ancient Age.
Still, in this era of upheaval, reports of
attacks by bio-engineered creatures
gradually decreased, and the world
appears to be recovering from
the Great Fall.
Scholars claim that the ancient ruins
themselves played some role in
maintaining the world’s climate
By destroying a great portion of them,
the world’s delicate balance was skewed,
and chaos ensued.
Moreover, due to the fact that Craymen
was a member of the Imperial Academy
at the time of his rebellion,
the Academy regards this fact with great
shame, and has abolished the position of
"Examiner," which was the rank that
Craymen held, as well as the act of
appointing Academy officers from among
Although we’re told that “most” of the Towers are inactive, I think the implication is that without Sestren to operate them, even the ones that are still online are no longer doing anything negative to the world.