Why did Thucydides believe similar events could happen again in the future?

Thucydides believed that similar events would recur in the future because he operated under the central philosophical presupposition that human nature is constant and unchanging.12

By analyzing the History of the Peloponnesian War as a diagnostic study of political and moral behavior, he aimed to create a "scientific" record of history. He argued that because human nature remains "what it is," the patterns of ambition, conflict, and societal degeneration he observed—such as the effects of civil strife or the consequences of unchecked imperialism—would inevitably repeat in similar ways throughout time.12

Consequently, Thucydides did not write his work for immediate public acclaim, but rather as a permanent resource for future statesmen and students. He intended for his analysis to serve as a practical guide, allowing future generations to recognize and understand these recurring human tendencies when they inevitably manifest again.123