The Mongol Empire is widely known as the hardest formable in the game. The reason for this becomes evident the moment you see what you need to conquer. To make this enormous empire you will need to annex much of the middle east as well as China and Russia while playing as Mongolia which is a country with a small economy and a lack of military resources. To make this empire you will need to play smart and be wise with your usage of your lacking money. First, try to ally either China or Russia (preferrable both). If they do not accept switch servers until someone does. If they do then justify war on the middleeastern countries you need and attck them. Also, if you are allied with China justify on Korea so you can take it quickly before anyone else does such as Japan. For your Central asian/middle eastern campaign first make 1k tanks and 300k troops. You should train them to mountain specialization. Once they are trained walk throught russia or chin and start the campaign. Over time each time you take a city if you have enough money make more and more tanks to take as fast as possible before Turkey or any other country takes what you need. Then Once you have all the land in the middle east and central asia break your alliance with whoever you are allied with. Then once the truce is over amass 20k tanks and 5 mil troops and invade Russia. If this succeeds then go after china with 5k more tanks and your done. Now you can flex your land and new title.