Common examples of secondary sources include academic books, journal articles, reviews, essays, and textbooks
I do not have your choices of "the following" Here are some reasons I learned: Christianity, empire was too big and became hard to manage, there were many nonromans attacking parts of empire- Goths, the emperors themselves were weak or insane intrigue was rampant.
A timeline is the presentation of a chronological sequence of events along a drawn line that enables a viewer to understand temporal relationships quickly. The term is also sometimes extended to mean a chronology that is tabular, year-by-year paragraphs or purely conceptual. Increasingly, timelines are illustrated in infographics combining text and graphic images for a better presentation.
The Incan civil war weakened the empire exhausting its resources and killing its fighters, thus leaving the door open to conquest by the Spanish
With their far greater numbers, they might have repelled the European forces meaning that they could have retained control of the continent
