People acquainted with Narayana - become Sri Vaishnavas. People acquainted with Shiva then they become shaivaites. Both have Vedic references to prove their point of view.
People interact with Iskcon they see Krishna as everything and they even ignore Vedas as pramana.
So do Muslims and Christians and all other religions as well. Most interestingly, people change from one religion to another, even within Hinduism!!!
All these are religions meaning they see GOD as definite thing. According to Vedas, anything that is definite is not Brahman.
When each one stick to something in specific, then it is difficult for them to see others view. Quite obviously, if one cannot see others view there is no chance of integration.
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Working of nature is such, having given scope for birth, nature then starts working for sustenance and destruction. Annihilation of some population on earth by fighting is a way of nature's working for destruction. Funny part is, other living beings have no thinking power, but human being even by having thinking power is not able to understand the working of nature and take remedial measure.