If you capture all of your enemy's cities, they can hide their army and navy in other cities, and you'll never be able to find it.
In Ikariam, it's already impossible to inflict significant damage on a player, unlike, for example, in Travian, where you can destroy an enemy city.
The inability to find an enemy army and navy makes the game boring for those who enjoy war.
I propose:
Adding a new mission for spies that will show the cities and number of units of the target of espionage stationed in other cities.
Moreover, it doesn't matter which player's city you're spying on; it shows the overall result (as is done, for example, when spying on messages).
What this will do:
This way, you can hide your army and navy only if they are constantly on the move. Otherwise, enemy spies will find out where the gold caravans are going to supply that army. 🙂 This will make wargames more interesting and lively.