The caravans as they are used now present some problems:
1) Unintuitive.
When I see a unit that is going somewhere, I expect a one time bonus when the unit arrives. Instead, I get a small percentage bonus every turn, regardless of where the caravan is.
2) Micro-managing.
While the caravan moves automatically, it still requires constant attention to prevent them from being killed by monsters. If they are killed, I need to rebuild the caravan, and resend it.
Even if the UI will make it easier by telling me which caravan was killed, it is still annoying.
3) Encourages city spam
Every minor city can send a caravan.
Caravan gives the bonus to the target city, so the more cities that can send caravans, the more food bonus you get in the major target city.
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My suggestion is to use trade routes instead of caravans.
Just like now, you will need to create a caravan unit and send it to a target city.
But instead of moving back and forth, when the caravan makes a single trip to the target city (or to the target and back to the source), the trade route will be created, and the caravan unit disappears.
For example, a city can have the following trade routes:
From city1: 40% bonus (active)
From city2: 30% bonus
From city3: 5% bonus
...
You can have as many routes as you want, however, only the first one with the biggest bonus will be active. The number can increase to Two after researching "advanced trade" or a similar tech.
If an enemy (monster or rival kingdom) blocks the route, you will be notified, and the active route will be changed to the next best unblocked route.
For example:
From city1: 40% bonus (blocked)
From city2: 30% bonus (blocked)
From city3: 5% bonus (active)
...
This solves all the problems, but still makes it important to patrol and protect your routes, and it will still be critical to protect the caravan in the first trip.
You will need less micromanagement. Even if a trade route is blocked, you will only need to remove the blockade, and not rebuild and resend.
City spamming will not help since every city has a limited number of active routes. And because this is a percentage bonus, you will get very little from sending caravans to a tiny city.
