Amazon is now the No. 3 Digital Ad Platform in the US

US advertisers will spend $4.61 B on Amazon’s platform this year, accounting for 4.1% of digital ad spending in the country.

Advertising is "now a multi-billion-dollar business" with hundreds of thousands of emerging and established advertisers: Amazon vendors, sellers, authors as well as third-party advertisers who want to reach the e-commerce site's customers.

Amazon also believe that their advertising business has 3 big advantages over the Google-Facebook duopoly's that will spur its already rapid growth:

1.     That's where shoppers go to buy: Consumers that go on Amazon are most likely there to buy. Moreover, ads that Amazon put in front of them are often seen as suggestions rather than real ads

2.     A huge and captive audience: Amazon has more than 100 million Prime subscribers or millions more that shop there without a subscription. That's still less than the billion-plus users on Facebook, but in this case, quality trumps over quantity.

3.     A safe environment: There's less risk for advertisers to have their brand associated with anything bad unlike with Google, Facebook or YouTube.

Source: https://www.forbes.com/sites/jeanbaptiste/2018/09/20/amazon-is-now-the-3-digital-ad-platform-in-the-u-s-behind-google-and-facebook-says-emarketer/#64b37cd03926