Why Arnor Failed as a State
So in lord of the rings, Aragorn, the titular returning king of the Third book/film, is the last descendant of Elendil, the first High King of Arnor and Gondor.
The entire plot is about how the royal family finaly, after all these years comes home to Gondor in the south from the cold, hard north, where the other realm of the Dunedain failed.
That said we are never really given a particularily detailed breakdown of why Arnor ultimately failed beyond the obvious military one(It was defeated by the rising power of Angmar before that too crashed and burned), the geographics one(the population never really managed to reach the level it could have, and that was before the plague), and the political one(the realm split into 3 lesser realms that squabbled).
On paper these seems easy enough reasons for why the northern realm crashed and burned, but once you actually start digging into it, it becomes pretty obvious that unlike Gondor, Arnor had some very serious fundamental problems that it never really managed to fix, which brought it down in the end.
1. It mishandled it's amazing geopgraphy
Looking at Arnor from above, it seems to have ALL the advantages. It has mazsive, open fertile plains, 2 great rivers, mild climate except for the far borth, clear, easy to defend natural boundaries, with the only open pathway into the realm being the hard to pass through corridor feom forodwaith.
Politically apeaking it was also set for success as the realm had managed to unify all the local peoples within it's borders underneath its banner, which they were content with for a very long time.
So with all of this in mind, where did Arnor go wrong?
It failed to harness it's rivers, that's how.
When choosing the place for capital for the new realm, one would expect it to be on one of the rivers, either at the mouth, or at an important spot.
The Dunedain chose to build the capital Annuminas at the great lake from whoch the Baranfuin/brandywine river originates from.
This isnt a... A terrible choice for a capital.
It allows the royal family to dominate the trade flowing up and down the river by controlling the spot where you can build ships, and have a massive riverrine fleet stationed in case of conflict.
So whats the problem?
The Dunedain never dredged either of their rivers, thats the problem.
Rather than wideding the bottom, to allow bigger, more usefull ships to pass up and down the river for transport of food, trade goods, and troops, Arnor instead did the exact opposite, and not only let natural fords stand, but built bridges that would prevent any trading river network from flourishing.
As far as i can tell, Arnor didnt have any particular noteworthy ocean navy, but even if Arnor was never going to invest into one such, the fact that they never did the work to make their rivers into a fountain of wealth, trade was one of the major reasons for their big decline.
But if they didn't invest into making their rivers more navigable, at the very least they would invest in horse power, in order for their people to travel quickly across the plain, allowing a caravan based trade netowork to do what rivers did not, right?
Well, no, and that leads me into my next point.
2. They Failed to turn into a cavalry based military, economic force, or political one
When the last king of Gondor(then prince) before Aragorns coming near a millennia later, came to destroy Angmar with a truly stunningly large relief force at the end of Angmar's power, he noted to his surprise just how perfect Arnor's plains would be for his cavalry in the task ahead of him.
And he was right. While it was the overhwelming numbers that won the day, it was the cavalry that was the main star, and allowed the army of the west to sweep over Angmar and end it forever with such ease.
With this in mind, it brings the question of why didnt the Arnorian Dunedain switch over to a completely horse based army, or at the very least make knights the shocktroops of the military the way Gondor did?
The reason seems simple enough.
Gondor was forced to fight endless wars against all of its neighbors and had to constantly adapt and change and improved, while Arnor was at peace for the better part of a millenium before it broke.
When the successor state of Arthedain had to adopt to new warfare, it always found itself outnumbered, and from the accounts of it's wars with Angmar, what they ended up doing was simply rely on powerful fortifications to fight defensive wara, and it's alliance networks to rally addiational troops.
Not strategies withouth merrit, but it's clear that Arthedain never managed to become a particularily great military powerhouse... But it could have if it had changed over to cavalry as the main feature of the army.
Instead they relied on what the numenoreans of old did. Arrow, sword and shield.
They no doubt had mounted troops of some sort, but it was clearly not their speciality just looking at how their successors, the rangers of the north prefer fighting.
But the fact is, Arnor should have had Cavalry centered armies from the very start, leaving behind the old Numenorean way of fighting the moment they realised all their future fighting would be on open plains.
However, this lack of focus on horses had another side effect. One that along with their squandering their rivers would contribute to another problem.
3. A lack of integration of the kingdom's ethnicities.
When Arnor broke off into 3 different realms, while the impetous was 3 sons fighting for control, when you look at the bigger picture, its clear that what actually happened here is that the 3 realms broke off very neatly along the kingdoms 3 main ethnicities, who each backed their own prefered candidate.
Arthedain, the biggest and strongest, centered around the heartland was populated by mostly ethnic dunedain, along with breemen as a smaller ethnicity.
Cardolan was ruled by a dunedain elite, but the ethnicity that dominated was the natice, pre numenorean population who were centered around the barrow tombs they would later be buried in(and would be corrupted by the witch king).
And finally Rhudar was also ruled by a dunedain elite, but the real power behind their revolt against the capital was the natice hillmen, who, being dissatiafied with Dunedain rule, and fueled by ambition decided to ally with Angmar in a bid for supremacy(only to later be exterminated by angmar once they no longer served their purpose).
What we see here is a very clear breakdown of the kingdoms, caused by a failed integration policy.
Clearly Annumias and later Fornost failed to bring these minorities into the fold successfully the way Gondor did eith its minorities, who became proud gondorians.
And we can in large part blame this on the capitals inability to project a sense of unity across the land. Which would have been easy to do if they had successfully tamed and harnessed their rivers, making all 3 corners part of a connected riverrine network, or had used horse based travel and trade as a matter of course to ensure everyone was connected into one economic and political policy.
Its very telling that the only people the Dunedain successfully integrated into their realm were the two minorities who lived right by the capital of Fornost(The hobbits and Breemen). Because these were the people who lived close enough that you could actually get there by foot at a reasonable time.
So with all of this in mind, there is a question to be raised. Why did Arnor squander all of it's natural advantages so badly?
Well i've gone over the military one. A stupily long amount of peace made the realm unprepared for innovation that allowed Gondor to become a powerhouse.
But no the real reason why the Arnorians would have seen no need to make changes to bolster trade, in and outside the kingdom, is due to a factor i have not gone over yet.
4. Trade mistakes.
Arnor and Arthedain both sit on an ancienct road used by the dwarves, both from across the misty mountains in the direction of rivendel, but also from gondor, and far more importantly for this dissection, during both Arnor and Arthedain's lifetimes, this road systwm would have been used by Khazad-Dum, Moria, at it's height.
All 3 directions heading to the Dwarves mines in the blue mountains and the great harbors of the Elven realm of Lindon.
It would in short, be one of the most lucrative trade routes of the age.
But, and this is critical, it was not a network Arnor actually had to do some work to take a advantage of.
They did not need to make caravans, or build trade fleets, ocean or riverrine. Hell, they didn't even need dedicated traders of their own.
They were middle men, who by virtue of sitting right on this route got to toll and harness the wealth this route generated withouth hacing to do any real work.
And that, ultimately was the problem. They didnt need to innovate. They didnt need to adapt and improve and put their land to full use, because all the wealth they could possibly use was there withouth work.
And that sucks, because clearly Arnor had A LOT of products they could have sold abroad. We can tell that just by looking at it's most prosperous successor state(the shire) and looking at what sort of technology they inherited from their original overlords.
The hobbits of the shire has paper mills, clockmakers, dye industry, matches, bound books, door knobs, integrated locks and latches, and on and on. Compare it to rohan, and they are centuries ahead in tech by our standards.
It's often easy to forget(give tolkien was clear that hobbits just did not move past a certain point in techonology) that by the standards of the day, the Hobbits are very technologically advanced compared to most... And ALL of that is things they inherited from their overlords.
Wheter Arthedain and by extension Arnor invented all of these technologies themselves(as there are a number of things clearly not found in gondor it cant all have been inherited from numenor), or they adapted it through Trade with Khazad Dum or Lindon, improved upon such foreign concepts, or kore likely a mixture of all of these, it's clear that Arnor had the capacity to make these, and by extension the fact they are still around after the kingdom fell, in the form of the hobbits being self sufficcient(otger than presumably the raw metal materials they trade for with the dwarves) means this was not some exceptional level of tech for the kingdom.
It was the kingdom's standard, and if they had been interested in actually exporting these things abroad, Arnor would probably have been more wealthy than Gondor by a far margin.
But they didnt. Because they didnt see any need to innovate their trade capacity in such a manner. Which in turn led to them not harnessing their lands capacity for cheap, easy transportations, which in turn led to them not integrating their people the way gondor(who's people are all connected through the sea and Anduin, and what comes with them), which led to them being far more divided than they should have been.
And while their long period of peace allowed them to overtake Gondor in so many things, when it came to military advancements, they were not only voefully behind, but when it came time to innovate, they lacked both the resources, and the spark to truly overhaul their military and tactics, instead relying on the same old classics until it brought the kingdom crashing down.
