What was once a niche event for Amazon to drum up sales during the summer shopping lull, Prime Day has now amassed into an industry-wide online shopping holiday, with retailers including Kohl’s, Best Buy, Target, and Walmart rolling out their own discounts. Amazon Prime Day, a two-day sales event that starts June 21, is expected to top $11 billion this year, according to the Adobe Digital Economy Index. But after a year of Amazon competitors sharpening their e-commerce business, the retail behemoth may have new competition riding its coattails this week, according to retail analysts. “Amazon is going to get the biggest slice of pie,” said Kristin McGrath, editor at RetailMeNot and Offers.com money-saving websites. “But shoppers will be weighing their options and working that to their advantage.” Read more at NBC News.