How did Hinduism survive in India but not in Indonesia or Southeast Asia (other than Bali and small communities here and there)?

 The spread and survival of religions in different regions are influenced by a complex interplay of historical, cultural, social, economic, and political factors. In the case of Hinduism, its presence in India and Southeast Asia can be understood through various historical developments:

1. **Historical Trade and Cultural Connections:** Hinduism had significant historical connections with Southeast Asia through trade routes. Indian merchants and traders traveled to Southeast Asia, contributing to the exchange of cultural and religious ideas. This facilitated the spread of Hinduism in the region.

2. **Indianization:** Southeast Asian cultures experienced a process of "Indianization," wherein Indian cultural and religious influences, including Hinduism, left a lasting impact on the local societies. This was particularly prominent in regions such as the Khmer Empire, Srivijaya, and Majapahit.

3. **Political Empires:** The influence of Hindu-Buddhist empires, such as the Srivijaya Empire and the Majapahit Empire, played a crucial role in establishing and promoting Hinduism in Southeast Asia. These empires adopted Indian cultural elements, including religious practices and art, contributing to the prevalence of Hinduism.

4. **Decline of Hindu-Buddhist Empires:** Over time, Hindu-Buddhist empires in Southeast Asia faced various challenges, including political instability, invasions, and internal conflicts. The decline of these empires resulted in the spread of other religions, such as Islam, which gradually supplanted Hinduism in many areas.

5. **Islamic Expansion:** The expansion of Islamic civilization had a profound impact on Southeast Asia, leading to the conversion of several regions to Islam. This expansion, often facilitated through trade and peaceful means, contributed to the decline of Hinduism in certain areas.

6. **Geographical Factors:** The geographical diversity of Southeast Asia meant that different regions were exposed to various cultural and religious influences. Some areas maintained a strong Hindu-Buddhist influence, while others saw the dominance of Islam.

7. **Cultural Syncretism:** In some Southeast Asian regions, Hinduism blended with local indigenous beliefs, creating syncretic forms of religion. This cultural blending resulted in the development of unique local traditions that may not be strictly identified as Hinduism.

It's essential to recognize that the spread and survival of religions are complex processes with no singular explanation. While Hinduism has retained a significant presence in India, certain regions of Southeast Asia, such as Bali, have maintained a strong Hindu cultural and religious identity. In other parts of Southeast Asia, various factors have led to the dominance of different religious traditions.