If I recall correctly, rice can sustain a much greater number of people per unit of land than any other crop, and this explains why East Asia is more densely populated than any other part of the world.
The big difference with rice is that you aren't dependent on the weather nearly as much as you are with corn and potatoes. Corn and Potatoes put out more calories per acre when the rains fall at the right times in the right amounts, but rice puts out those calories regardless of the weather.
Ultimately you can only sustain a population as large as your food output at the end of a two or thee year long drought.
Sugar cane and sweet potatoes also produce similar calories per acre, depending on the soil, climate, etc. Sugar also has the advantage of being durable to ship. It could be produced in high volumes on tropical plantations and shipped to Europe.
Before bulk ocean shipping of food, population was generally limited by calorie production in the local area.
