ORIGINAL: Feralkoala
It appears that there is no penalty to having foreign armies (particularly two as rapacious historically as the Russians and Spanish) fight on your land--you might as well rent it out like an arena [8|]
That's not quite the case. Rapaciousness is configurable by the player - you can set your units to "plunder", which offsets some of their upkeep costs. You can actually do this in your own territory, as well as in enemy territory. In this case, neither of them did any plundering on my territory. So you could say they were on their best behaviour.
Russia got access because they were willing to ally with me during the fight against France - they probably hoped I would help against Spain too, but noone ever ASKED me to attack Spain, and I couldn't see any point.
When I originally gave Spain access, it was to get their colonies, which I really wanted. I didn't really think they would send so many troops up, or fight the Russians for so long. After the access term ended (it only goes for a year), I didn't give them another one (they weren't willing to pay me with anything I wanted). For a while they were violating my territory, but once my armies got back from France (late 1808), I issued an ultimatum every time they violated my territory, and they stayed out.
Now, it is true that I try to abuse game features (before Eric made it much harder, I was encouraging play testers to HIRE armies and fleets from AI countries) - so we end up with a better game. The question is:
- what should the affect be of having other countries march through (or have battles on) neutral territory? Is it simply that it makes foraging more difficult in the areas they are in? Or should there be some other penalty?
- although I didn't do it, I could have been providing depot supply to both armies! Should we make that impossible?
- perhaps my ally should gotten all huffy over me giving Spain access, and demanded that I either break my treaty with Spain, or break my alliance with them? We don't have that feature (which would be cool, so I will recommend it for the first patch), but even if we had, I think a good Russian player would have swallowed their angst and kept Prussia onside. (Remember, at that time, France had beaten Austria, and had Spain helping them against the remaining allies, Britain, Sweden and Russia.)