Between the Aes Sedai and the creatures believed to be some new kind of Shadowspawn that the defenders of this new continent came to be known as the Armies of the Night.
These were the descendants of creatures brought back from parallel worlds via Portal Stones, during the first thousand years after the Breaking, probably in an attempt to find aid against the real Shadowspawn.

If grolm weren't brought to our world until after the Breaking, then how did Lanfear know how to handle them with conventional weapons ? It's possible I suppose that she met one during the AoL, but if she had to kill it, surely it would have been with the Power, OTOH, maybe these things were just kept in zoos in the AoL and people just knew about them.

It was during this period that all remaining Shadowspawn on the continent were eradicated.
The knowledge that allowed their procurement by way of the Portal Stones however was lost.

I have a slight problem with this knowledge being lost, given that the technique was still known during the first thousand years after the Breaking. Also, it wasn't just a matter of one secretive AS acting alone, such an operation would surely have required many Seanchan AS working together.

Animal Handlers
After his successful conquest Luthair adopted them into his own armies.
Animal handlers or riders in Seanchan are known as morat or one who handles, a morat'grolm for example is a grolm handler, a trainer is called der'morat as in der'morat'grolm the word der means experienced or master and often denotes rank.
To become an animal master and thus earn the prefix der, requires a certain level of seniority.

The social order among the handlers of exotics is as follows :

1. der'sul'dam
2. sul'dam
3. der'morat'raken
4. der'morat'to'raken
5. morat'raken
6. der'morat'torm
7. morat'to'raken
8. der'morat'lopar
9. morat'torm
10. der'morat'grolm
11. morat'lopar
12. der'morat'corlm
13. morat'grolm
14. morat'corlm

This list, and indeed the entire chapter, entirely fails to mention s'redit!

Torm :
Appearance : A cross between a horse-sized cat and a lizard. Bronze scales, six-clawed feet that can grip the stones of the road; and three eyes.
Intelligence : The most intelligent of the Seanchan exotics, after damane of course, are the torm.
Intelligence quotient well above that of a very bright dog.
They can come close to our level in certain areas of problem solving, such as maze tests.
Diet : Torm is primarily a carnivore but will subsist on a plant diet for as much as three or four days if it must. If deprived of meat longer, the torm becomes increasingly hard to control as it seeks to hunt.
Reproduction : They bear live young and nurse them always in single births.
Advantages : As riding animals their speed and endurance are superior to that of a horse, but they are particular about their riders.
Disadvantages : Cannot be put to hunt.
It will turn on a potential rider.
Once it has found that one rider, the torm will not allow another to mount, If that rider dies, it takes some time to get a torm to accept another.
Unsuitable for protracted fighting.
Fighting frenzy if in battle for too long. Rarely turns on its rider during one of these frenzies, but it will strike at anyone else within reach.
Uses : They are primarily ridden by scout units.
Further Info. : A torm will always strike at any corlm in reach and while morat can keep the attack from coming to actual combat they are simply never used together. They are not widely available, and are hard to replace.

Corlm :
Appearance : Sometimes as much as eight feet tall, with a long neck and a sort of double crest on its head, hair resembling the colour pattern of some house cats.
Fur usually gray black or brown, extends to the tail which it flattens out for stability while running.
Averaging three hundred pounds, tiny forearms usually held close to its body.
The beak is large appearing oversized.
Diet : Carnivore.
Reproduction : Female lays her eggs one at a time, but they often do not hatch.
Advantages : The corlm uses its beak for killing.
An extremely efficient killer, able to track prey with both scent and hearing. It is unmatched as a tracker and can outrun a man in short sprints and can equal a man over long distances.
Disadvantages : Used singly as they do not tolerate each other.
Further Info. : Responds to both spoken commands and whistles pitched above human hearing.

Lopar :
Appearance : Premier fighter of the exotics weighing between fifteen hundred and two thousand pounds.
No external ears.
Leathery hairless hide which is dark brown or a pale reddish hue.
Six toes on both front and rear paws all with very large retractable claws.
Sometimes rear upon their hind legs when fighting to a height of as much as ten feet.
Intelligence : Intelligence higher than that of a dog, probably equal to that of a torm
Reproduction : Lopar mating resembles a battle.
Births are always in pairs.
Advantages : Able to sprint as fast or faster than a horse.
Premier fighter of the exotics.
Well able to pull a man from horseback.
Disadvantages : It tires easily over long distances.
Uses : The lopar is used as a guard animal and as a ferocious fighter in battle.
Normally fitted with a soft leather coat or barding cover with overlapping metal plates to protect the spine, central chest and belly.
Blood frequently use lopar to protect their children.
Further Info. : Usually placid, and even friendly

Grolm :
Appearance : Weighing in at three hundred to five hundred pounds grolm are the size of large bears but with the gray green coloration and skin texture of very tough frogs. Like the torm they have three eyes.
When walking grolm appear almost awkward moving with a waddling motion but all traces of awkwardness vanish when they run.
Diet : They consume their own dead.
Reproduction : Rare for more than one offspring in a litter to survive.
Advantages : They are very hard to kill.
Nonfatal wounds seldom incapacitate them and they heal rapidly.
They also have very good vision a keen sense of smell and are extremely territorial.
Uses : Grolm are used in battle, though only against lightly armoured opponents to break holes in an enemy line which will be quickly exploited by human soldiers. They can also be used against cavalry as horses often panic in their presence unless trained to tolerate them.
Further Info. : In their natural environment they are apparently pack animals.
Grolm are controlled with spoken commands, hand signals, and the use of a small piercing whistle-like flute.
Among morat'grolm it is a matter of pride to use only the hand signals and the flute, perhaps in distant imitation of the way the Blood communicate.

Raken :
Appearance : Raken has a body considerably longer than a horse's and about equal in girth, with leathery gray skin and large powerful wings much like those of a bat.
While it is not used as a weapon the raken often lashes the tail in anger when perched or on the ground and has been known to accidentally break the arm or leg of a careless morat.
It normally crouches rather than standing erect, it stands erect only when alarmed or preparing to fly.
Intelligence : Intelligence is roughly equivalent to that of a horse.
Diet : It is an omnivore though apparently perfectly content with an all-plant diet.
Reproduction : An egg layer, the female raken lay one egg at a time.
Advantages : Maximum flight speed is three to four times the speed of a horse.
A raken will fly even if injured or ill and may be ridden to the point of its death.
It can perch comfortably even on vertical surfaces
Uses : Primarily used for scouting and carrying messages, carry two people if they are small.
Further Info. : Fliers are all either women or smaller than average men, and often ride double one behind the other in a specially constructed lightweight saddle.
Long distance for a raken is three to four hundred miles.

To'raken :
Appearance : Like the raken except that it is much larger and is mottled brown in colour rather than gray.
Crouches when on the ground.
Intelligence : It has the intelligence level of a horse and is an herbivore.
Reproduction : Eggs are laid one at a time.
Advantages : The value of a to'raken lies in its strength and endurance.
Known to fly over a thousand miles at moderate speed.
With one morat up a to'raken can carry an additional one thousand pounds or more of cargo as far as two hundred miles.
Disadvantages : Unlike the raken which can simply throw itself into the air, a to'raken must run as much as one hundred paces while flapping its wings before launching itself from level ground.
Neither as agile in the air nor as fast as raken, its maximum speed is a little more than twice that of a horse, it also does not perch on vertical surfaces.
Injured to'raken does not fly well, often refusing to fly farther than a safe landing point.
Uses : Transport animal, seldom used in battle.
Further Info. : It does not perch in trees however large.
To order a morat'raken to fly a to'raken would entail a loss of face for the flier a fact which even the Blood recognises.