This is the 2472nd most frequent Chinese word.
戰爭
War.
The context of '戰爭' in this sentence is its general meaning as 'war' or 'conflict' as a noun.
戰爭是一種不可避免的社會現象。
War is an unavoidable social phenomenon.
Here, '戰爭' is used to refer specifically to a particular instance of war, a concrete example rather than the general concept.
那本書描述了一場虛構的未來戰爭。
That book describes a fictional future war.
In this case, '戰爭' is used metaphorically to describe a strong confrontation or conflict, in this instance in the economic domain.