The Seleucid dynasty was a Hellenistic kingdom founded by Seleucus I Nicator after the death of Alexander the Great in 323 BCE. It controlled a vast territory that included parts of modern-day Turkey, Syria, Iraq, and Iran. The dynasty played a significant role in the spread of Greek culture and influence throughout the region. The Seleucid Empire faced numerous challenges, including internal strife and external threats from rival kingdoms. It eventually fragmented into smaller states, leading to its decline. The dynasty lasted until the rise of the Roman Empire and the emergence of the Parthian Empire in the 1st century BCE.