Sugar was once a major driving force for colonization. Sugarcane and sugar beats are the only plants that can be extracted for sugar efficiently. These plants grow in tropic environments, so they were not found in Europe. Needless to say, the price for sugar was astronomical hundreds of years ago.
Sugar is fairly commonplace now. The type of sugar we buy is sucrose, which is a disaccharide formed by glycosidic bonding between glucose and fructose. By using heat and trace amounts of acid as a catalyst it is possible to convert sucrose back to fructose and glucose monosaccharaides, which are very useful in candy making.
Sugar contributes much more to dessert making than sweetness. In baked goods it provides tenderness by interfering with gluten formation by competing with gliadin and glutenin for binding of water. It also browns by carmelization at temperatures above 338°F (when sugar begins to decompose and melt)and Maillard browning at lower temperatures when protein is present. It prevents lump formation in starch thickened sauces if added directly to the starch, stabilizes egg whites, raises coagulation temperature of protein mixtures, and aerates batters and doughs.