The Seleucid Empire was a Hellenistic state that emerged after the death of Alexander the Great in 323 BCE. Founded by Seleucus I Nicator, one of Alexander's generals, it encompassed a vast territory that included parts of modern-day Turkey, Syria, Iraq, and Iran. The empire was known for its cultural diversity and the spread of Greek culture throughout the regions it controlled. At its height, the Seleucid Empire was a major political and military power, but it faced challenges from rival states and internal strife. Over time, it fragmented into smaller kingdoms, ultimately succumbing to the rise of the Roman Empire and other regional powers by the 1st century BCE.