Once the player has formally met another civilization, they can perform diplomacy at any time. For example, if the two civilizations are on friendly terms, the player can ask to trade units and/or technology for gold and vice versa, or request opening of national borders in order to freely explore in the other civilization's territories. The player can also use the diplomacy menu to request help in a war against a third civilization, or formally declare war on any civilization in which they engage diplomacy.