@Kayriel
You forget something, in our world too there were brigans and pirates yet merchandise has crossed the world.
Sometimes the merchants became pirates, to become merchants again
When you buy something you risk meeting thieves on your return routes, or on the transport of goods, because an object before arriving at the user/consumer is passed into the hands of many merchants.
it's not just big cities and port cities where customers are, very often the object continues its way into the countryside.
The lords are not everywhere and cannot guarantee security between cities and in villages.
Moreover in this case, it is more a city state than a city belonging to a country, so the way is free for all type of people.
It is surely several group of merchants gathered in a city between several kingdom/Empire, they took advantage of the location and the inhabitants enjoy the protection of these merchants and the city grew prosperous.
These merchants are essential for the surrounding countries, so no risk for the merchants and in any case the merchants together are surely strong enough to fight a country on their own, even several if they use diplomacy and their money in addition to their army
They came with small armies, the attackers had come to buy and had an army to bring back their purchase.
They did not have enough money, so their army is used to attack that of those who had the coveted objects.
The experts who protected the princess of the other country were poisoned why?
Because they were stronger than the two young villains of the same group, if the two young had been stronger they would have killed them themselves.
So we can also say that the princess of the other country had a small army (personally i think they were rank 9, this is a real princess not like the friend of MC, so experts from rank 9 should be normal for her guards).
And she herself is of rank 8, but even the friend of MC disguised as a boy of rank 10 thinks she is hiding something.
it is also possible that two groups are currently attacking them even 3, these groups would have gathered to find the objects faster, won the battle more easily and in the end will share the rare objects which have been bought by the princess of the other country .
They maybe even recruited mercenaries.
There is perhaps only one very powerful group, which does not think to need help,
so much it thinks to have the advantage.
It is the emperor who wanted an objects, therefore it surely send a small army to be sure of him