Answer: All time periods must be studied because no one period will cover all the themes
Step-by-step explanation:
All time periods must be studied individually, to begin with. Each era in human history has its own milestones and events that characterizes it, so that what takes place in one era does not happen in another.
It is said that something is universal when it is popularly known. Each era in human history has its popular events, which then, as societies progress, are related to future events and history start to take a more consistent form.
However, it is impossible to build a full knowledgement about it without having particularly studied each era, through different authors.