How to defend against an early invasion in Civilization VI

Among the new changes in Civilization 6 is the ‘Casus Belli’ system, which increases people’s distaste for war as you progress through the eras. Although declaring war on your neighbor for a perceived slight may be acceptable in the Ancient Era, nobody is going to stand for that sort of unwarranted aggression come the Renaissance.

This is a major change to diplomacy, and one of the main knock-on effects is that the AI will attack early, when diplomatic penalties for doing so are low. Although early attacks are always expected at higher difficulties, where the AI likes to leverage its starting bonuses against the player, early AI aggression has now seeped down into lower difficulties so that any player can find themselves staring down a terrifying invasion force while they’re still gathering their wits.

It’s tough to deal with, especially when you’re not expecting it, and it can be off-putting. Luckily, there are a few things you can do to make sure you can survive the early game onslaught, and perhaps even use it to catapult yourself into a winning position.

Use Terrain to Your Advantage

Ever since Civilization 5 changed up the combat system, mastering the terrain has been a big part of winning wars. In the early eras of Civilization 6, especially when your opponent has a numbers advantage, knowing how to use your terrain is a huge boon.

If you’ve scouted out the nearby area you should hopefully have an idea of where your neighbors are going to be coming from. Be prepared by having your ranged units placed on hills, so they don’t waste time moving into position when the enemy arrives. If you can plug up a chokepoint with units or, even better, a city, then you can force your enemy into a disadvantageous situation.

My early settlements frequently take local terrain into account. Settling near a chokepoint will make it harder for the AI to flood your territory with units, making numbers matter much less. Generally just settling in rough terrain will make it harder for enemy units to reach you quickly, giving you more time to respond.

Upgrade to Archers ASAP

Possibly the most important defensive step you can take is upgrading to Archers as soon as possible. Compared to your starting ranged unit, Slingers, Archers have longer range and are significantly stronger on both attack and defense. The tech to unlock them is relatively cheap, and you can earn a 50% boost to it pretty easily. Having even 1 or 2 Archers can stop an invasion force in its tracks.

Getting Archery quickly means earning the 50% Eureka boost, which you can do by killing an enemy unit with a Slinger. I recommend making a Slinger as your second or third build in a city and then sending it out with your Warrior to hunt barbarians. Your Warrior can help weaken an enemy Scout or Spearman, then leave it on red health for your Slinger to finish off. That same Slinger can be upgraded to an Archer once you’ve got the tech, and hopefully will even have a promotion by then, enhancing its combat potential.

Archers don’t need to be your very first priority, but should come pretty early. Since Slingers are pretty cheap to build and upgrade I tend to build 2-3 and upgrade them to Archers once the tech is researched, but if you have other things you want to work on you can wait until Archery is researched before building your second and third units. Either way, make sure you get that first Slinger out ASAP, position it to kill a barbarian, and then make your way down the tech tree to unlock Archery.

You Don’t Need Walls, But They Help

Walls have seen a major upgrade in Civilization 6, making them incredibly strong at defending against early aggression. Building Ancient Walls in a city will increase its strength, allow it to make ranged attacks, and give it an extra HP bar that’s resistant against most melee attacks. Trying to take down a city that has walls in the Ancient and Classical eras is a significant challenge, and more often than not having walls in your city will be enough to repel an early AI invasion.

That said, it’s also important to know that while walls are useful, they’re certainly not necessary. Good use of terrain and units will help keep enemy units from even getting in range of your city. Building walls is purely a defensive measure, and won’t help out your economy, hurting you in other ways further down the line. This is especially true in cities that aren’t likely to come under siege, since they’ll see almost no use from their walls.

I find walls most useful when I don’t have confidence in my ability to keep enemies from getting close, or when they’re quick enough to build that my economy won’t take a hit. In cities which don’t struggle for production it’s not a bad idea to build walls since you might not have much else to build anyway. Cities that are on mostly flat terrain or push right up against another civilization’s borders also benefit from walls, since they’re likely to come under siege no matter what you do.

Cities that are in rough terrain, far from the front lines or simply don’t have the production output to build walls quickly should skip them in favor of other defensive or economic measures. When deciding whether or not to build walls, weigh up your options carefully and think about what you could be doing instead.

Know Your Enemy

It’s almost inevitable that you’ll be attacked early by someone, but knowing who is most likely to do so, and what they’ll be attacking you with, can be a big help. Some AI are more likely to attack than others, will attack earlier or later, and might have special units or abilities that will give them an advantage.

If a civilization has an early game Unique Unit, then they’re highly likely to use it in war, and more likely to be aggressive early on. Leaders like Gilgamesh, Cleopatra and Montezuma who can build their unique units almost straight away are among the most aggressive and deadliest civilizations to face. If you meet them early, it’s worth putting a bit more effort into your defences than usual.

Some AI are less likely to attack. Gandhi likes to keep the peace, and Tomyris, despite having strong military bonuses, hates unwarranted aggression. Starting near these AI means you can generally breathe a little easier. Don’t be too passive, though. There’s always a chance that they might attack anyway.

Knowing who is likely to attack you isn’t just about knowing whether or not to build up your defenses: it also allows you to know which direction the threat is coming from. If you know that one of your borders is safe and the other is dangerous, your defences will be in the right place when the attack inevitably comes.

The Best Defence is a Good Offence

Of course, if you want to make absolutely certain you’re going to win your early game wars, consider taking the initiative. The AI is attacking you because there are no diplomatic penalties for doing so, so you can take the same path. Attacking your neighbor not only prevents their early invasion, in a way, if you pull it off you’ll also knock out a competitor for the rest of the game and kick start your own game.

Going on the offense requires a bigger army, and you will definitely need Archers for it. Spearmen or Heavy Chariots are also a big bonus if you have time to get a couple out, but otherwise an excess of basic Warriors can help you get a city or two before walls start going up. Obviously if you have access to early game unique units then those are bound to do strong work.

Be mindful, though, that if you have multiple neighbors and send your army against one of them, you might be leaving yourself vulnerable to counter attacks from another direction. It’s a mistake to go on the offense unless you’re confident that you can fight a war on two fronts, or that you won’t need to.

Don’t Neglect Your Military

However you choose to play the game, the most important thing is that you don’t neglect your military. Between the more aggressive barbarians and the early game war declarations, you’ll need at least a few units to keep yourself safe.

Once you’ve got a few basic military units, you can keep upgrading them throughout the game and not have to worry too much in future. Getting a reasonable army early is an investment that you don’t need to put too much into to maintain. Even peaceful builders need something to defend themselves with.