Although there is no structured support for diplomacy within the game, alliances are one of the most powerful things within the game.

Players who have no alliances will quickly find themselves surrounded, and holding the short end of the stick.

There’s also a bit of an art to it - depending upon the person you’re negotiating with, you might have to be willing to come to some difficult compromises. Intermingling of resource gathering buildings to some degree is fairly common with strong partners.

There’s several ways of going about it, I prefer the proactive method - that is: I contact people I’m near, that I’d like to ally with.

Sometimes this will be an active partnership - eg: assistance in defending/attacking a common enemy.
Other times it will be a simple non-aggression treaty, and agreeing to split up some given bits of territory.

In any case: good communication is the key to ensuring your neighbors know your intentions, and don’t interpret (say) you moving 50 light cavalry near the border as you planning an invasion.

Some players will initially agree to an alliance, only to break it with little or no forewarning. This can be a very effective tactic, especially if you choose your moment carefully. However, remember that players can, and will remember this in future games - as the saying goes “Once bitten, twice shy”.

One of the worst things, conversely, is to aggressively build near someone’s existing territory when there is plenty of other unclaimed resources near by (and closer to your territory) without communicating first.

So, just to summarise:

Do:

• Communicate early, and often with neighbors.
• Try to negotiate terms agreeable to both, even if that means compromising, and giving up (say) some mountains which you hadn’t built on yet.
• Keep your alliance partner(s) informed of what you’re doing, especially if you are building or moving military units near their territory.

Don’t:

• Build towards someone aggressively without communicating, unless your intention is to create a conflict.
• Break an alliance unannounced, without first considering the potential ramifications (especially for your future games)

Following these few guidelines will ensure you have a much higher chance of surviving to prosper and flourish.