I consider advanced warning of an attack everything to surviving in Civ. Unless you can afford to have a large standing army and the costs that entails (as well as directing your build attention away from improving cities) I like to have a few good units in each city and rely on intelligence to give me notice of impending doom There are several ways of getting this information of course, so I've put the methods I can think of below. I would welcome any others. -Scout OK an obvious one, but important and I'm surprised how many people, espec on multiplayer, don't use them. I ALWAYS put ships around my island or coast as soon as I can to get advanced warning of ships heading my way. Presuming you have a reasonable standing army, you can mobilise and protect. Not forgetting, attacking these transports of course. Caravels were made for this job! I always try and keep a few even in late game so I can check out opponents land without their consent! Aircraft are also great for this since they can do it without open borders and cover a large distance. If I have open borders I always try and stick a few scouts in my opponents big cities too - noticing a huge army on your border is *too late*. Open borders is of course, no suggestion they won't attack... -Cancelling Agreements ...but of course cancelling open borders and the like is a suggestion they're up to something. The AI usually only does this when they fall out with you, but humans (in multi) do it because they know you are watching. Again, the amount of people who don't use this, espec in multiplayer, amazes me. -Changing Civics In either multiplayer or AI games, players like to get the benefits of civics which give xp to their units if they are likely going to be involved in a war. Don't buy an excuse from someone who says "I just want to build a few troops with good xp". They are thinking of a war (unless they have a suspicion you are about to attack!). Clearly, the civics Police State, Vassalage and Theocracy come under this banner. -Power Graph Overall power is certainly influenced by the amount of military you have. You can more often than not, see sudden spike in the graph when someone has started producing lots of military units. Certainly, if it is very sudden and in contrast to the way there cities are developing, there is a likelihood they are gearing up for war. -Pearl Harbour I call it this because the AI or human will have a port or two in which they have a large number of warships and transports, often with a growing number of units. To detect this of course, you need to be close enough to see. Caravels are perfect for this task. I would welcome more suggestions!