An increasingly common ingrediant, especially in commercially prepared food items. As it was once only available in the form of cane sugar, it used to be a luxury item, imported from the subtropics at great expense. With the rise of colonialism, however, this all changed, and the price of sugar was dramatically reduced, as it could be produced in plantations using slave labor.
Only recently has sugar been cheap enough to use as an ingredient in foods. Previously, it was used in other forms: as a preservative, as a form of decoration (a practice which still survives in the form of gingerbread houses), as a spice (i.e. used in small quantities for flavoring; as an ingredient, sugar is used in larger quantities as a primary component of a food), and for medical purposes.
Source: Sweetness and Power