Final answer:
The Long Twentieth Century refers to the late 19th century to the late 20th century, marked by major historical events and technological advancements. The American Century describes the period when the United States became a global superpower through industrialization and economic growth.
Step-by-step explanation:
The Long Twentieth Century: The dates that could be described as 'The Long Twentieth Century' refer to the time period from the late 19th century to the late 20th century. This period is marked by important historical events such as the rise of nationalism, decolonization, the World Wars, the Great Depression, and major technological advancements.
The American Century: The term 'The American Century' refers to the period from the late 19th century to the late 20th century when the United States emerged as a global superpower. It was during this time that America experienced rapid industrialization, economic growth, and exerted significant influence on the world stage.