There were several reasons why Lincoln feared about his reelection in 1864. Firstly no Presidents since Andrew Jackson before him had won the election for the second term in office. Secondly Lincoln knew that his embracing of emancipation did not go down well with the voters of the North. These were the reasons for his fears.
1200BC and declined around 400BC
The most useful is documentary evidence. Things people have written. Old newspapers, personal accounts, even things like letters, bank records, govt. records, etc. For fairly recent history there are photographs and even films and videos.
But even writing only goes back about 6000 years. Before that there is archaeological evidence. From studying the debris of ancient civilizations historians can determine what their buildings looked like, what they ate, who they traded with, what they thought was
