The original nuisance was the goblins. Short, never passing 5'6 in height they were not terribly strong, fast or smart, but were curious, clever and aggressive. As the people of Heartland built to the north and northeast human-goblin encounters were more and more common. Even when they avoided goblin encampments and territories they were attacked
The worst incident was when the kingdom was one hundred and ten years old. A town north of Fort Blaine was swarmed by a goblin horde that was unprecedented before. Roughly seven hundred went over the town, killed the men and boys, raped the women and girls then killed them.
Some think the order of rape and then kill wasn't observed for all the females...
Seeing that the goblins were more of a threat then believed a general, Terry Smith, marched an army forth to the forest with a hundred magicians. He ordered the forest burned.
The fire and smoke flushed out the goblins who were ill equipped to fight military forces. He repeated this several times, decimating the forests, hunting and logging in the area for almost two hundred years, until the goblins were either killed or driven out of Heartland to the west. Since then goblins have only been reported, credibly, being in their borders twice, the last four hundred years ago.
While Smith was formally chastised for burning the forests the crown did not do anything more, just happy the situation was solved.
The other major monster problem was the pigmen. Ranging from 6'3 to 7'4, the huge beasts were much more of a threat then the goblins. Encountered in the south-west seven hundred and thirty years ago they started to spread north east. Even more aggressive then the goblins and with the size to cause much greater harm, they were much more willing to slaughter males and kidnap and rape females.
It didn't take long before Heartland responded. General Walter Stone took the magical poleaxe that would become known as Dragon Slayer and moved his army to meet them. The pigmen wore leather armor and only held primitive weapons; clubs and stones tied to sticks. Some even held rusted axes and hammers scavenged from others.
The two forces clashed and despite better equipment and training the Heartland army was pushed back. The pigmen had enough numbers and strength to continue their march. Reinforcements arrived not long after and Stone was able to block the advance, making a stalemate. The two sides clashed again and again as villages and towns caught in the struggle were raided and pillaged by the pigmen.
The fight against the pigmen lasted almost four months before the push back fully started. The numbers of the pigmen dropped while reinforcements kept streaming into the Heartland army. Over the course of a month they pushed them back past the boarders and into a magical temple.
After the pigmen were killed it was found that they were a man made creation. The mad magician who made them presumed he could control the thousands of the monsters he had made. However the enraged beasts enslaved their creator, putting to work to make more of them as they marched forth. By the time the military arrived he was a shell of his former self. The man was arrested and sent to prison.
He would die there four years later.
The pigmen were eradicated; they could never impregnate women no mater how much they tried and the magician only ever made males. The threat was ended forever as the notes and temple were utterly destroyed.
While today Heartland still has monster problems they under better control then before. And they have defeated monsters before.
They can again.