I'm as new as it gets

[gmaharriet]

Now other civs say they heard about my surprise attack on them. I warned them!!!!

Just warning them isn't enough. There are two types of warning. 1) "You have troops within our borders and they MUST be removed."...the lightest warning which they may (or may not) ignore. 2) "Remove your troops or declare war.", stronger warning and to which they either leave or declare.

If they don't leave and don't declare, you are still NOT at war. The best case is if they declare on you...it gives you "war happiness". If they don't declare and you want war, you must declare on them before attacking so as not to get a rep hit. When you do this, check first to be certain you have no units in their territory (including boats in their waters), or it is considered a sneak attack.

 

[MAS]

Declaring war when you have units in their territory is a sneak attack. This will cause a reputation hit, and a bad reputation will make making trade deals and alliances in the future more difficult.

To prevent this, first declare war, via the diplomacy screen then move your units in their terrain. (beware you don't have an exploring boat or other unit inside their terrain that you forgot about)

If they declare war on you, its their problem, and anything goes.


If the AI is moving units in your terrain, for other reasons than an obvious sneak attack. it is probably because they want to settle on unclaimed land on the other side. Or because they want to fight a civ on your other side.

The best way to prevent this is to settler the land yourself first. Should be easy on lower difficulty levels. Prioritize claiming unclaimed land at the start!

Punishing the AI for moving units inside your land won't help. The AI isn't programmed to respect borders, they simply don't understand.

If you want peace, make sure you own a pice of land bordering coasts. Preferably with only one, short, non-water border. Or even better, owning your own continent. That way, you are sure that the only business the AI has in your land is a sneak attack.

Even if not going for a conquest victory, many players would still make a point of conquering their starting continent.

 

[Sashie VII]

many players would still make a point of conquering their starting continent.

Absolutely. Owning your own continent gives you more benefits than sharing it:

1. You get more cities.
2. You have no land border to constantly watch.
3. You get more resources.
4. Odds are you'll get any resources you ever need for the game (RNG luck aside).
5. You're basically immune from conquest defeat.

IMHO anyway