In another attempt to introduce a little-known contender to the ancient world scene, King Cersobeptes of Odrysia, I've started this timeline. This Thracian warlord was bent on uniting the myriad Thracian and Dacian tribes into a single state, and hoped to create a small empire on the black sea. He planned to modernize his army, and seize Byzantium. His mistake, however, was to call upon his enemy Phillip II of Macedon to help settle the end of a long conflict between the tribes. He chose not to engage Phillip whilst their forces were equal, but after he was weakened by years of war. The Macedonian would end up subjugating Cersobeptes and and other Thracian warlords, paving the stage for a lineage of Thracian Princes ruling only in name.
Here's a timeline where things happen a little differently.