It seems to me that one thing that could be changed is how land and castles are added to the game.

As I understand it, there are only 2 ways to produce extra land in the game, and only 1 way to produce castles.

Land:

Exploration - This can only produce (as per the game guide) up to 3 land per hour, or up to 6 land per hour with Farseeing.
The creation of new kingdoms

Castles:

Building them

In regards to land, the second method is essentially irrelevant since it only contributes new land if a Kingdom is attacked to below 10 land.

To address the obvious, Attacking doesn't produce land or castles, it is simply a transference of the land that's been explored and the castles that have been built.

I wish I had more suggestions on how to increase but I'm hoping others here might have some ideas. Here's one that I had:

A temporary NPC Kingdom pops up on occasion that everyone can attack together, like a world boss. Everyone who participates is awarded land and castles based on a number of factors such as damage dealt, percent of army used, and other things that would work.

Participants would also win resources from the plunders of war, ex: double the gold, wood, and iron of the army sent, and 10x the upkeep of food based on the army sent.

This could create an influx of resources, land, and castles.

The details are irrelevant in the current state of the idea, but if there are details that you think might make this feasible then please let me know!

If you think it's a good idea or a terrible idea, either way I'd love to hear your thoughts.