An Amazon Fashion ad. Facebook/Amazon Fashion An unlikely company has suddenly catapulted to the top of the fashion world: Amazon.

Amazon is now the biggest seller of clothes online in the US, with its apparel sales totaling $16.3 billion last year, Bloomberg reports.

That's more than the combined online sales of Macy's, Nordstrom, Kohl's, Gap, and Victoria's Secret parent L Brands in the same period, according to Bloomberg.

Amazon is now second only to Walmart in terms of overall apparel market share, according to Morgan Stanley analysts.

The company's rise as a leader in apparel sales has been swift and relatively quiet.

Amazon made one of its first major pushes into the category 10 years ago with the purchase of the clothing website ShopBop. Three years later, Amazon bought the online shoe retailer Zappos for $850 million.

An Amazon Fashion ad. Facebook/Amazon Fashion Over the past couple of years, Amazon has ramped up its investment in fashion by launching its own private-label clothing brands and sponsoring the first New York Men's Fashion Week.

The company has also hired executives from luxury fashion companies, such as Julie Gilhart, the Barneys New York fashion director whom Amazon reportedly hired as a consultant, and vogue editor Caroline Palmer.

An Amazon Fashion ad. Facebook/Amazon Fashion Also in the past few years, Amazon has started to shift its fashion strategy toward offering more high-end designer names, such as Zac Posen and Stuart Weitzman.

That shift has had some industry experts scratching their heads. Luxury fashion websites are typically well-merchandised and highly curated — not things for which Amazon is necessarily known.

An Amazon Fashion ad. Facebook/Amazon Fashion But Amazon's strategy appears to be working.

Morgan Stanley analysts estimate that Amazon's apparel sales grew by $1.1 billion in the most recent quarter, while the department stores Nordstrom, Sears, Macy's, Kohl's, JCPenney, and Dillard's collectively lost $225 million in apparel sales in the same period.

An Amazon Fashion ad. Facebook/Amazon Fashion Department-store executives have blamed declining apparel sales on the weather and on consumers' changing shopping habits, which in recent years have gravitated more toward big-ticket items like televisions and vacations over clothing.

The apparel market has only grown 1% annually in the past 15 years, according to Morgan Stanley.

But department stores' loss so far has been Amazon's gain, according to Morgan Stanley analysts.

"We expect online (primarily Amazon) will continue to take share from department stores, but at an accelerating pace over the next five years given new evidence that Amazon is gaining traction in fashion," the analysts wrote in a recent note.

In a 2012 interview with The New York Times, Amazon CEO Jeff Bezos gave a simple reason that Amazon was investing in fashion: "Gross profit dollars per unit will be much higher on a fashion item," than with cheaper products, he said.