In the last decade, the biggest change in the U.S. economy has been the rapid adoption of e-commerce. Once considered a mere curiosity, digital is quickly becoming the preferred shopping method for many Americans. Partially fueled by the pandemic, retailers that invested in the digital channel are reporting tremendous growth, and holdouts are being forced to move into the space or risk becoming irrelevant.

Of course, you can't mention e-commerce without including Amazon (NASDAQ: AMZN). The company essentially wrote the book on e-commerce, and early shareholders have been among the biggest beneficiaries. Obviously, the stock has made investors a lot of money over the past decade, creating many millionaires in the process. But just how much would you have had to invest a decade ago to be a millionaire today?

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A decade of success

It's difficult to fathom now, but Amazon is a relative newcomer to the list of the most valuable companies. The company did not crack the list of the top 20 largest U.S. companies by market capitalization until 2014. Since then, it has continued to drive higher, growing to become the third-largest company in the United States (trailing only Microsoft and Apple).

Unlike Apple, which declared a 4-for-1 split earlier this year, Amazon has not split its stock in the last decade. This is a reversal from Amazon's earlier mindset, as the company declared three stock splits in less than a year and a half during the tech boom of 1998-1999. Another clear difference between Amazon and its mega-cap tech peers is the former has never paid out cash dividends. Because of these two things, determining how much Amazon stock you needed to buy then to be a millionaire now is a straightforward exercise.

At Tuesday's close, a share of Amazon cost a little over $3,200, so $1 million worth is 312 shares. The share price for Amazon was $180 a decade ago. So if you bought 312 shares for a total investment of $56,160 back then and held on, your position today would have a total value of a million dollars.

Amazon's run isn't over yet

The biggest argument against Amazon's stock today centers on two separate -- yet interrelated -- issues.

The lazier of the two arguments is that, due to its immense $1.6 trillion market cap, the stock is too big to continue rewarding long-term investors. This argument that "the easy money has already been made" reached a fever pitch when the stock first hit the $1 trillion mark, and the stock has grown 60% higher in less than two and a half years. America is still in the early innings of the shift to e-commerce: In the third quarter, the U.S. Census Bureau found that e-commerce was only 14.3% of total retail sales. Although the pandemic has increased adoption in the short run, the trends underpinning the growth of e-commerce are not reversing anytime soon. As the largest digital vendor in the United States, Amazon is in the driver's seat to benefit from this continued shift.

The second argument is stronger, as it centers on valuation. But even that line of attack falls apart under further inspection because Amazon has been growing its bottom line just as fast as its stock price in recent years. Through the first nine months of 2020, Amazon has increased sales 35% over the prior year and earnings per share nearly 70%. Amazon's PEG ratio (which compares future earnings estimates to today's valuation) is currently 1.25, a modest premium that's more reminiscent of a value stock than a high-growth company.

It's been a great decade for Amazon investors -- and the long-term drivers are in place for future gains.

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John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Teresa Kersten, an employee of LinkedIn, a Microsoft subsidiary, is a member of The Motley Fool's board of directors. Jamal Carnette, CFA owns shares of Amazon. The Motley Fool owns shares of and recommends Amazon, Apple, and Microsoft and recommends the following options: long January 2022 $1920 calls on Amazon and short January 2022 $1940 calls on Amazon. The Motley Fool has a disclosure policy.