Multiplayer is a completely different world from singleplayer, and while playing MP may improve your SP, the inverse is only true to a certain extent. Humans and the AI act completely differently, and it's wise to be aware of the many differences this causes before joining a game. Wars: understanding when fighting will and should occur Humans will rarely leave a war unless their objective has been reached. If you're invaded by a foe with rifles against maces, they're not going to accept a few gold for peace. Conversely, if a human suddenly offers you peace, they most likely have a very pressing reason to do so. If you've been on the defensive and just got your first cossack, it's better to re-conquer all of your old cities than let your opponent fortify them! Unlike AI's, humans are usually very well prepared for wars if they chose to attack. If a competent player declares war on you, expect a sizable stack of well promoted units, not a few improperly promoted out of date ones. Humans are also much better at defending than the AI; you'll need a good stack to launch a successful attack, not just your one first tank. Preparedness: knowing when an attack is coming, and being ready It's important to always be prepared for an attack. Humans are much more ruthless than the AI, so they will attack you if they see an opportunity. When defending, there are three things that need to be protected: 1. Cities 2. Resources 3. The high ground Cities Properly dividing military resources is a game of prioritization. Cities are usually the most important target that must be defended - especially in games with city elimination on - but your one source of metal is more valuable than a worthless tundra city. In order to protect cities, always have multiple roads running to and between them. Even before the discovery of Engineering, reinforcements will travel twice as fast. The 50% movement increase along roads is a compelling reason to research Engineering early. Keep a sizable garrison of units in your front cities, but only those you need for happiness in cities that will never be attacked. The AI likes to defend its core cities better because it values them higher. Humans are effect enough at attacking that you'll need to move all of the units to the front that you can. Keeping your main force hidden behind a front city can allow for surprise "ambushes" of an attacker. If what was one turn ago a lightly defended city is suddenly armed to the teeth, the attacker may either move on, hoping for a weaker target, or attack the city even when it is impossible to take. Retreating is always a good option if an attack is doomed to fail. Defensive improvements - walls and castles - are effective in forcing the attacker to either have overwhelming force, or bring siege gear in order to take down cities. Attacking and defending units will be roughly equal if they are similarly promoted, but a +100% bonus will swing the odds greatly in favor of the defender. While siege gear is clearly enormously important for the attacker, it is equally important for the defender. Being able to soften up an attacking stack before it attacks will help to equalize the effects of collateral damage from the attacker. Beware, though, that if you attack with your siege gear without being able to kill of the enemy's units, you present the opportunity to heal and return at full strength. You will have more time to reinforce, yet your opponent's units will live. Using siege units when you cannot kill the stack is sometimes a necessity for survival, but it should be done only as a last resort. Resources There are a variety of wars to protect resources. Founding a front city in front of them so that they won't be threatened is a good idea if you can defend it. If that's not an option, the best defense is usually to keep a small responsive stack - including a fair number of catapults - in the area to kill an attacking stack. The high ground Unlike the AI, people think. They will have no trouble cutting one road into a city, and won't attack your City Garrison III riflemen with macemen. Similarly, humans won't walk up their stack across flatland if they can avoid it. Always take precautions to cancel out the easiest routes of attack, including those with the greatest defensive cover. Chopping your forests not only provides a quick production benefit to your cities than can help your expansion, but it removes necessary defensive cover from the attacker. Forests and jungles, the best cover in the game, can luckily be removed. Hills, on the other hand, cannot. Hills next to cities provide valuable cover for your opponent, so it's helpful to position units of your own on them to hold the high ground. A similar approach can be taken to forests and jungles which you haven't been able to chop yet. It is imperative to chop all of your forests and jungles near the front, especially those on hills. Always be mindful of the terrain in front city placement. A city on a hill will get a +25% defensive bonus that cannot be removed to units in it, and an additional +25% to archery units in it. A city placed next to a hill, on the other hand, is vulnerable to the enemy fortifying their stack on it while they bring in reinforcements and their siege gear pounds down your city's defenses. A city behind a river gets a defensive bonus against units attacking across it, but units attacking out of it will also suffer this penalty! Knowing when an attack will come - the use sentries Another important aspect of defense is knowing when an attack will come. Expanding your borders is an excellent way of seeing an incoming stack earlier, but positioning sentry units outside of your borders can have an even better effect. If you see a "surprise" attack coming ten turns early, you'll have amble time to whip defenders and fortify your position. Sentry units are best positioned on hills, both for the increased visibility and the defensive bonus. Having a "sentry net" of units extending the length of your border will usually provide enough warning to respond to a potential attack. Roading the front Finally, always remember to "road your front." Having multiple roads leading to, between, and from your front cities will make life much easier for the defender. Roads extending forward will allow for the easier use of catapults and defensive stacks. Attacking: taking down human-defended empires Because of the way the system works, attacking in Civilization IV is somewhat difficult. An attacker must bring enough siege equipment to knock down the walls of a city and do collateral damage, enough attacking units to actually take the city, and a variety of other units to provide cover for the stack. If your opponent has not chopped their forests - a mistake often made by nonladder players - two Woodsman II units will provide excellent cover for your troops. The attacker has a number of advantages when they launch their attack: 1. Knowing when they intend to attack. 2. Knowing where they intend to attack. 3. Knowing that they intend to attack. Even if a defender knows that an attack is coming, their newest cities may not be properly prepared. If the attacker launches their attack as a surprise, often because of a double move and the lack of an effective sentry net, they will have a major advantage. Similarly, many players are simply unaware that an attack is coming at all. The most common form of nonladder game is the FFA, or free for all. Some player expect a buildfest, and they can often be caught with only one units defending all their cities. While this tactic may hold in singleplayer, against a decent opponent, this person will quickly be annhilated in multiplayer! Similarly, if the defender has a number of cities on the front, the attacker can pool all of his forces in one place while the defender's are split. Staying equally distant front two cities while cutting roads between them is an excellent way of keeping the defender's troops separate. All of the aformentioned advantages can be neutralized through the use of a good sentry net. A devious attacker can, however, use a mounted unit promoted with sentry to "break" a sentry net. The promotion, which grants its unit an additional tile of visibility range, allows the attacker to skirt around the edges of a sentry net unseen. In this way, the cunning attacker can hunt for weaknesses they can exploit while remaining unseen. Another benefit for the attacker is that he attacker can split his stack into more than one, while the defender of a strategic tile cannot. The attacker can thus protect himself against collateral damage far better than the defender. The downside of this tactic is that each mini-stack is provided with less defensive cover. Units heal far slower in an opponent's territory - 5% per turn, compared to 10% per turn in neutral territory and 15% per turn in friendly territory. Bringing a unit with Medic I or II can often lead to a far improved rate of success. This is one of the reasons that aggressive civs are so popular for early eras: even with only one promotion, they can access either Medic or an anti-unit promotion on their melee units. Remember that retreating is always a good option if an attack is doomed to fail. It's better to back off and heal your units than to provide your opponent with experience and Great General points. Lastly, never attack an opponent armed with metal primarily with swordsmen. While the AI doesn't seem to build enough axemen, humans have no problem doing so. Building: Balancing expansion and tech Growing and expanding Multiplayer is often about expanding as much as possible early on. While eight cities in BC times may not give you a sustainable economy, having four will lead to a stronger economy than three. Having more early cities than your opponents will allow you to get more military than them, and have a stronger economy later on once your cottages have matured. Larger cities can work more tiles and be more productive than smaller cities, so growing them as quickly as possible is usually a good idea. Use Hereditary Rule and a large enough garrison to keep them happy, then grow them to the health limit. Building granaries early provides a drastic increase to growth, as well as a useful health bonus. Do not bend your civ around getting a single wonder; waiting to get a second city in favor of stonehenge will only serve to criple you. The pyramids are a similarly often overvalued wonder: they're nice to have, but you'll often want to go with Herdditary Rule anyway, which comes early enough if you focus on it. Because workers and settlers slow growth, chopping forests and slaving to speed these builds can provide a useful boost. Be wary of too much slaving though, as the happiness effects start to add up. In a free for all with good players, it's usually a good idea not to appear to be the strongest nation. Keep a sizable military, but slave enough to stay out of first place early on. My limited experience with FFAs with good players indicates that not being a target is extremely important. Technology and productivity Having a large force of workers improving the land around your cities provides a massive boost. Working improved tiles is far more productive than unimproved tiles, so it's important to get tile improvements up and running as quickly as possible. The most productive tiles - resources, cottages on floodplains, etc. - should be connected first. It makes no sense to irrigate a tundra tile before a grassland! Similarly, workers are required to "road the front" around any potential front cities. Cottages are extremely important in remaining competitive financially. Many nonladder players inexplicably do not build cottages, perhaps because of habits learned in Civ3. Floodplains are an excellent candidate for cottaging, as the city gains both a commerce bonus and a food bonus by working them. While cottages are a necessity, it is also imperative to build improvements intelligently. Do not cottage every tile, as it will then be impossible to work mines and other high production tiles. Expanding a city's borders at least once is very important in order to claim its "fat cross." Monuments, religion, the Creative trait, and stonehenge all offer a quick and cheap way to do so. Spreading religion is already very important because of the benefits of various religion civics, and so it's often a better choice than building a monument. The traits Aggressive Very important early on, the Aggressive trait allows double promotion units early, and triple promotion units later. The bonus is more significant than an additional 10% strength bonus to each melee and gunpowder unit. Combat I unlocks both Medic I and the powerful anti-unit promotions. Industrious Industrious's faster wonder building effect can swing the race for a crucial wonder into the Industrious leader's favor. The bonus production to forges is also very useful on what is otherwise a quite expensive building. Spiritual Being able to often switch civics without a penalty - especially into Slavery or Nationhood in case of an emergency - is a great boost. The cheaper temples are somewhat less powerful. Organized Organized is often considered to be one of the worst traits. Financial is generally a better choice, but organized becomes more powerful later in the game when more high-cost civics are available. Financial A great trait, financial is the most powerful early on. Cottages on a river of hamlets get a +50% gold increase, while post-Printing Press towns only get a +20% increase. Like industrious, financial can swing to race to crucial technologies - including those which enable wonders - into the financial leader's favor. Creative Creative is a powerful ancient trait for free border pops. It provides additional score, allowing for access to the "fat cross" without religion or a monument, wreaks havoc with non-Creative leaders' borders, and provides a useful defensive bonus quickly. Expansionistic Expansionistic is another strong ancient age tech. Almost all cities will want a granary, so it's extremely helpful to have them at a lower cost. Since the happiness limit effectively vanishes with hereditary rule, a health boost is also always nice. Philosphical A very powerful trait, philsophical allows full use of great people. Whether they are for culture bombs, academies, or free techs, it's nice to have them faster and cheaper. Protective Protective is a useful trait for both the builder and the warmonger. The builder can use it to more easily maintain control of his empire, while the attacker is required to build less defensive units, allowing him to build a more powerful offensive stack. Charismatic Charismatic provides a number of useful bonuses. The happiness bonus can allow for slaving without regard to the happiness penalty, and allow cities to grow larger in the period before Hereditary Rule. The bonus to unit promotions is also incredibly helpful. With the change to barracks, Charismatic leaders are now the only ones who can access triple promoted units with the Pentagon. Imperialistic Imperialistic leaders have an enormous bonus to production of settlers. With less time spent on settlers - or more settlers built in the same time - Imperialistic leaders have a massive expanding bonus over leaders without this useful trait. The bonus to great generals provides a helpful boost in the quest for these powerful great people. For further reading, I encourage people to read Fried's The Fine Art of the Siege. I learned many of these tactics from that article, which goes into greater depth about both attacking and defending.