Final answer:
The rise of Indian nationalism and the political ideology of Hindutva had the most significant impact on the perception of Hinduism in the 20th century, promoting a more unified and less pluralistic view of the religion.
Step-by-step explanation:
The most impactful event on the perception of Hinduism in the 20th century arguably includes the rise of Indian nationalism and the consequent political ideology of Hindutva. This movement led to a re-interpretation of Hinduism that sought to define it not as an ongoing interaction between diverse traditions, but rather as a set of definitive practices and beliefs. The promotion of Hindutva was part of a broader nationalist effort to unite India against British colonial rule, and to redefine Hinduism as a monolithic culture, distinguished from other religious and cultural impositions. The impact of this movement has been profound, influencing political discourse, shaping Indian history textbooks, and altering the perception and practice of Hinduism both within and outside of India.