What did people eat?
Throughout most of history, most people never got enough to eat, and many people starved to death. Food was much more expensive than it is today, and governments helped people out less than they do now. Even farmers often went hungry when city people took all their food for themselves as taxes, or if the weather was bad and storms or diseases ruined the crop. Children went hungry more than their parents, because if the parents starved the children would probably die soon anyway, where if the parents lived they could always have more kids.
When people could get food, the food people ate varied a good deal from time to time and from place to place. So you'll need to read about each time and place separately. There are some things all these times and places had in common, though.
First, one reason food was so expensive was that there was no refrigeration or freezers. It was very hard to keep food from going bad. People did a lot of different things to preserve food. The most important thing was to store dried grain: wheat and barley and millet and rice and corn. They also dried fruit to make raisins, dried figs, dried beans, dried corn, and dried apples. They pickled eggs and vegetables, meat, and fish in brine (salty water) to make pickles and garum, a fermented fish sauce. They fermented grape juice and apple juice and barley to turn them into wine and cider and beer. They made milk into yogurt and cheese. They smoked meat from pigs to make ham and bacon, and they preserved meat in honey.
Second, because it was so hard to carry things from one place to another without canals or trains or trucks, most people could only eat local, seasonal food. If there was a shortage of food because of bad weather or crop diseases, or because soldiers had wrecked the crops in a war, people starved. People in different places ate very different foods, and what they ate changed over time as new foods arrived from other parts of the world. Central Asians brought pigs and cows and apples to West Asia around 7000 BC; dates first came from West Asia to Africa about 4000 BC. Wheat first reached China from West Asia about 2500 BC; chickens first reached West Asia from India about 1000 BC. Bananas reached Africa from India around 500 BC, and rice left India for West Asia and Europe a few hundred years later.
The strength of Central Asia and the rise of the Silk Road between 500 BC and 1500 AD encouraged a lot more trading of food all across Asia. More Central Asian cinnamon and pepper began to reach Europe and China. Bee-keeping traveled from West Asia to China, and peaches, lemons, and oranges returned in the other direction. Sugar spread from India all over Asia and even as far as Europe and North Africa; coffee and tea spread across Asia from Africa and China.
When Europeans began sailing across the Atlantic Ocean to the Americas about 1500 AD, they brought sheep and pigs and chickens, wheat, beehives, sugar, and apples with them. A little later, it was tea and coffee. From the Americas to Europe, they sailed back with potatoes, tomatoes, corn on the cob (maize), turkey, chili peppers, squash, chocolate, and avocados. They brought American sweet potatoes to China, where poor people started to eat sweet potatoes as their main food.
Central Asian food
Native American food
Central American food
West Asian food
Islamic period food
Food, by Fiona MacDonald and others (2001). For kids, facts about food from all over the world. A little preachy.
Food and Society in Classical Antiquity, by Peter Garnsey (1999). Garnsey has written a lot about ancient food, and is an expert, but he writes very clearly.
Food in Antiquity: A Survey of the Diet of Early Peoples, by Don and Patricia Brothwell (1998). Pretty specialized, but the book tells you where foods came from, and how they got to other places, and what people ate in antiquity. Not just Europe, either!
Food: A Culinary History from Antiquity to the Present, by Jean Louis Flandrin, Massimo Montanari, Albert Sonnenfeld. (1996). Hard going because it is translated from French, but Flandrin was one of the world's great food historians.