As Rebecca mentioned in this video, food and farming has changed dramatically in the last century. The number of farmers, the size of farms, and the technologies we use have all changed in many ways. Part of this is due to the Green Revolution.
The short and sweet story of the Green Revolution is connected to scientist, Norman Borlaug. (If you want to read more look at the links at the bottom of this post.) While working in Mexico in the 1940s, he developed a disease resistant strain of high-yield wheat. This was one of the factors that led to Mexico becoming one of the top exporters of wheat in the 1960s. Increased research and funding produced more of these crops which are used successfully worldwide with the exception of Africa.
The high-yield crops developed in the Green Revolution are reliant on fertilizers and irrigation. However, their success and increased has resulted in crop homogeneity. Crop homogeneity, means a lack of variety. When crops are too similar they become more vulnerable to certain pests, which increases the need for pesticides. This is one of the factors contributing to the chemicals we find in our food.
If you want to learn more about what chemicals are in the food you eat and how it may adversely affect your health, do a quick google search and talk to a health professional. If you are concerned about a specific product, you can look it's Food Score on EWG's website or healthy living app.
The Green Revolution & Farming Sources