Final answer:
The American burger, as fast food, originated around the turn of the 20th century due to the need for convenient meals for factory workers and concerns about meat quality. BBQ practices and European immigration significantly influenced American cuisine, with refrigeration and transportation advancements paving the way for the modern fast food industry.
Step-by-step explanation:
The idea for the American burger did not come from "Pulp Fiction's" reference to the "Royale with Cheese" or from the American Army's ration meals. Instead, Americans first began eating hamburgers as fast food around the turn of the 20th century, often as a convenient option for factory workers who needed a hot lunch. Suspicion around the quality of ground meat at the time led to the modernist design of hamburger joints which aimed to assure customers of safe and hygienic food preparations. This modernist architecture, although it reads as nostalgic fun from the 1950s today, actually pre-dates the 1950s.
BBQ restaurants and practices also played a role in shaping American cuisine, especially where climate and economic conditions made BBQ a practical way to prepare and preserve meat before refrigeration was invented. Beef became the most popular BBQ meat in regions suited for grazing cattle, but this varied across different parts of the U.S.
Another significant factor in American culinary history is migration and ethnicity. European immigrants introduced many food staples to the American diet. Over time, industrial developments, such as refrigeration and transportation improvements, led to the availability of a wider variety of foods, and fast food became more entrenched in American culture.