“Farmers and laborers ate earlier because they were up really early, and the elite were eating later in the day because they could sleep in. Breakfast and supper were kind of like glorified snacks, often leftovers or cornmeal mush, and there was not a lot of emphasis placed on these meals. Dinner, the main meal, at which people did tend to sit down together and eat, was really not the kind of social event that it has become. People did not emphasize manners, they did not emphasize conversation, and if conversation did take place it wasn’t very formal: it was really about eating and refueling. That’s the time where there are very blurry lines between what is and what isn’t a meal, and very blurry lines between what is breakfast, dinner and lunch.

Then, with the Industrial Revolution, everything changed, because people’s work schedules changed drastically. People were moving from the agrarian lifestyle to an urban, factory-driven lifestyle, and weren’t able to go home in the middle of the day. Instead, they could all come home and have dinner together, so that meal becomes special. And that’s when manners become very important, and protocol and formality. It’s really around then that people start to associate specific foods with certain meals.”

– http://blogs.smithsonianmag.com/food/2013/10/why-do-we-eat-cereal-for-breakfast-and-other-questions-about-american-meals-answered/