What is the most fundamental difference in the conception of empire in Thucydides’s world as opposed to Alexander’s

What is the most fundamental difference in the conception of empire in Thucydides’s world as opposed to Alexander’s, and what role do these different conceptions of empire have in justifying war

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What is the most fundamental difference in the conception of empire in Thucydides’s world as opposed to Alexander’s, and what role do these different conceptions of empire have in justifying war?