How to win a domination victory with a militarily weak empire?

Ultimately, to win a domination victory, all you have to do is to conquer the capital that all the other Civilizations have set up in the game. It's not easy but that is what makes it so fun. But you can do it if you set your mind to it. You can have a Surprise War of a Casus Belli, the choice is yours. Within the reals of a Casus Belli, there are a variety of wars you can wage.

You can have such things are War Weariness and Combat Stats to help you in your cause. There are specific strategies you can try in each of those that can help you to win a victory in domination. You can also emply Pillaging or War Formations and implement the strategies that will help you to dominate. Once you get a feel for how to perfect one of those or how to play them all into the picture, you'll be well on your way to victory.