Amazon ensures existence of Flipkart and or Snapdeal
While there is a belief that Flipkart/Snapdeal/both compete against Amazon, it may not be true.
A Flipkart/Snapdeal will never match/compete with Amazon, it will all but be a significant alternative — better than all other (soon to die) alternatives.
Amazon is popular (and will win, until its true), while Flipkart and Snapdeal will belong to the alternative space. The consumer has chosen (popular) and will look for alternatives to reiterate his/her choice (a function of great ux, price, availability, selection). The rest will die (good money on bad) leaving the alternate space without a long tail.
To win in the alternative space (the second best investment), one will need either a superior product or superior economics.
Amazon, unfortunately for its alternatives, has the best product yet, and the cheapest capital in e-commerce.
This is the starting point for the alternatives. Unsurprisingly, this is evident in other spaces as well.