The Mongol Empire forged by the chieftain Temüjin, who took the name Genghis Khan in 1206, is the largest in known history. It stretched from Korea in the east to present-day Poland in the west, spanning 13 million square miles and containing over 100 million people. That's bigger than Rome ever was, bigger than Alexander's Empire, and bigger than the paltry British Empire (although not as globe-spanning). Civilization V didn't ship with the Mongols as a playable civ, but Firaxis was nice enough to include it as free DLC last month. I've played as the mighty Genghis Khan for more than a few games and, true to his nature, all of them have been victories in which I've destroyed my fellow civilizations, crushed them under my foot and made them bend a knee to the might of the Mongol Empire.
Based on my conquests, I've compiled a few tips on how to effectively wage war in Civ V. Some of this is curtailed to playing with the Mongols but all of it will help you win wars playing as any civilization. Keep in mind that these tips are by no means an exhaustive list of all of the ins and outs of strategy in Civ V but mastering these concepts will give you a basis on which to wage your perfect conquest. I've also concentrated on winning wars in the early to mid-game so that you have the tools needed to establish an empire to rival that of Ghengis Khan.
Take a look at the embedded video examples which illustrate exactly what I'm talking about with in-game footage.
Secure Strategic Resources Early
In Civ V, you must have certain resources at your disposal before you can build the most powerful units. The first of these is horses, which only appear on the map once you've researched the Animal Husbandry technology. If horses aren't near your first city, make sure that you settle your second one near a stand of wild horses. Once your workers build a Pasture, your civ will be able to build not only the Horseman unit, the first powerful cavalry in the game, but also the Chariot Archer.
It's a good idea to continue building, or capturing, cities near Horses because once you enter the Medieval era, you will want to pump out a lot of Knights. Or, in the case of Mongolia whose unique Keshik mounted archer replaces the standard Knight. These units excel at charging in, releasing a volley of arrows and then retreating a safe distance away. Which brings me to my next point ...
Fire Ranged First
Archers and Catapults are early ranged units and they can be really strong in battle, but only if you make sure to fire them before you charge in with ground troops. On the open field, Archers loosing arrows on a poor barbarian is a sure way to secure victory. Firing ranged first is especially important when attacking other civilizations. Cities, especially those pesky city-states, are strongly fortified and will decimate an army if you attack headlong without any ranged support. Maneuvering your ranged units so that they can fire without the risk of a counterattack is super important, because if an enemy unit attacks them they will be wiped out without much of a fight.
That's why the Keshik is so valuable. With a movement of four hexes, you can move in and out without the fear of retribution.
Beat Up on Barbarians
Like in previous Civs, barbarian units can spawn randomly in any area that isn't controlled by more civilized people. These barbarians are a nuisance, as they sometimes capture your unprotected workers or plunder your lands, but they can also be a resource. Think of destroying the barbarian hordes as training for when your armies will face harder foes. Every fight your units get into yields experience, even if they lose more hit points than the foe. When you earn experience, you can pick promotions which vastly improve the effectiveness. The more fights you get into, the better your troops are. Plus, the 25 gold you get from dispersing barbarian camps really starts to add up. So grab a sword and fight the Horde. There's only enough room in this world for one bloodthirsty Khan.