How did commerce, conquest, and religion spread Indo-Iranian languages?

The spread of Indo-Iranian languages was significantly shaped by the interplay of commerce, conquest, and religion, which facilitated their use in both administrative and literary spheres.1

• Conquest and Administration: Political expansion played a crucial role in establishing these languages as administrative tools. For instance, Old Persian served as the official language of the Achaemenian dynasty starting in the 6th century BCE. Similarly, an eastern Middle Indo-Aryan dialect was utilized by the Mauryan emperor Ashoka for his chancellery in the 3rd century BCE.1
• Religion: Indo-Iranian languages became deeply embedded in the literature of major world religions. Indo-Aryan languages were used for texts related to Buddhism, Hinduism, Jainism, and Sikhism, while Iranian languages were central to Zoroastrianism and Manichaeism.1
• Commerce and Cultural Exchange: Trade and cultural contact helped extend the influence of these languages far beyond their points of origin. Indo-Aryan influence, particularly through Sanskrit texts and lexical borrowings, reached deep into Southeast Asia, including areas such as Indonesia and Thailand.1