I don't understand why...

[Spiker22]

it's not possible to ask other players (AI or human) to stop the stealth actions like spying on me via the diplomacy system. I mean I clearly know who did the attacks, but there's just no such an option in the request lists to ask them stop those attacks. I can't kill the enemy unit becasue I don't want to get involved in a war against them, so all I can do is repel the stealth unit.

[Michiel B de Boer]

Station some stealth units in your cities and your main empire entry roads, then kick the enemy spies out when you see them with a military unit.
You can also use spies on them, you know ? (easy way to capture cities)

[bad0cat]

In diplomacy screen you can request that an enemy "withdraw his forces." What the manual (and the strategy guide for that matter) doesnt tell you is that this refers to *all* enemy forces, including stealth units. If you request an AI to withdraw and they say "yes" then they will remove all their units, including stealth units (most of the time anyway )

If this doesnt work you can try:

1) Build "The Agency"
2) Put spys on all major roads/choke-points of your civ

...and if all else fails....

Build a stack of 12 tanks and roll over the spying bastards; this is how my all my "diplomacy" works - try it.

Hope this helps!

[Dale]

I must agree with bad0cat here.

I'll ask once on haughty to withdraw. If they don't go I ask angry to withdraw. If they're still in within another 5 turns (10 turns in total) I declare war and roll the buggers!!! That's my diplomacy method for ANYTHING! If I don't get what I want I just roll in and take it.

Does this make me a "Militaristic evil genius" player then?

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Rommell to a sub-commander outside Tobruk: "Those Australians are in there somewhere. But where? Let's advance and wait till they shoot, then shoot back."