Any story makes less sense when learned in bits and pieces.
History is no different. By the time you graduated high school or college, you'd studied King Tut, the Trojan War, the Bronze Age, the rise of the city-state and the Exodus. Chances are you studied these subjects in different years, out of different textbooks. You probably can t put them into chronological order in your own mind. Furthermore, you probably spent twice as much time on American history as you did on the history of the rest of the world combined.