The difference is that Thucydides was attempting to make his reasoning and evidence clear in a way that was quite unusual among ancient authors. Look at Herodot

The difference is that Thucydides was attempting to make his reasoning and evidence clear in a way that was quite unusual among ancient authors. Look at Herodotus. Entertaining as heck, interesting stories. Extremely dubious scholarship. Or, skipping forward half a millennium, Suetonius. Libel and gossip. Or take Dionysius of Halicarnassus and his penchant for speechifying. It’s not so much about being unbiased as it is about backing up your opinions with actual evidence, rather than just telling a story.