Complex sentence: Subjugation of Macedonia was part of Persian military operations initiated by Darius the Great (521--486) in 513-after immense preparations-a huge Achaemenid army invaded the Balkans and tried to defeat the European Scythians roaming to the north of the Danube river.
Split into simpler sentences: Subjugation of Macedonia was part of Persian military operations initiated by Darius the Great (521--486). In 513-after immense preparations-a huge Achaemenid army invaded the Balkans and tried to defeat the European Scythians roaming to the north of the Danube river.