Betting against Amazon.com, Inc. (NASDAQ:AMZN) has been mostly a losing game. Yet the company still has major challenges. Keeping up the growth is certainly going to get tougher, given the scale of the revenue base (which was over $135 billion last year). It’s really about the law of large numbers.

The good news for AMZN stock is that the company has been able to successfully move into other major markets. A standout example of this is the cloud-computing business, which is known as Amazon Web Services (AWS). This segment has not only added substantial revenues, but has also been the main source of cash flows.

But when it comes to AMZN stock, the driver will likely remain the core e-commerce business. The fact is that retail spending is massive — and of course, undergoing disruption. Just look at the many ailing traditional brick-and-mortar operators like Macy’s Inc (NYSE:M), J C Penney Company Inc (NYSE:JCP) and Sears Holdings Corp (NASDAQ:SHLD).

Yet, the U.S. market will not be enough. Rather, for the momentum to continue with AMZN stock, the company will need to dominate various foreign markets. And a notable one is India.

According to data from IMRB International, anywhere from from 450 million to 465 million of the population has access to the internet. Oh, and based on research from Forrester, the spending on e-commerce is forecasted to reach nearly $64 billion by 2021.

OK, so what about Amazon’s role? Well, for the most part, the company has made early investments in India — and because of this, there is a sizeable footprint in the country. It definitely helps that the firm has deep experience with logistics but also has the leverage from offerings like Prime and Kindle platforms.

Competition And AMZN Stock

As should be no surprise, competition is getting more intense. Consider the bold moves from Masayoshi Son, who operates SoftBank Group Corp (OTCMKTS:SFTBF). During his storied career, he has certainly made savvy investments, such as with Yahoo and Alibaba Group Holding Ltd (NYSE:BABA).

But now Son has a massive war chest. Keep in mind that his Vision Fund has nearly $100 billion.

No doubt, this should be a worry for holders of Amazon stock as Son has a priority on e-commerce. To this end, he recently agreed to invest about $2.5 billion in Flipkart, which is a top player in India.

Son’s investment has come after a $1.4 billion infusion from firms like Tencent Holdings Ltd (OTCMKTS:TCEHY), eBay Inc (NASDAQ:EBAY) and Microsoft Corporation (NASDAQ:MSFT). He also knows how to build e-commerce businesses in emerging markets, as seen with the incredible success in China.

Now this does not imply that Son will ultimately prevail. But then again, he has the financial resources to wage a brutal fight. And besides, there are other mega tech operators that are doubling down on India, like Alphabet Inc (NASDAQ:GOOGL, NASDAQ:GOOG) and Facebook Inc (NASDAQ:FB). They could leverage their mobile apps to capitalize on the e-commerce opportunity.

Bottom Line on AMZN Stock

One of the biggest threat to Amazon is that the company is not laser-focused like the multiple e-commerce players in India. The firm is moving into so many new categories that it is tough to keep track of them.

Perhaps the most striking example of this is the $13.7 billion acquisition of Whole Foods Market, Inc. (NASDAQ:WFM). This is not only the largest deal for Amazon, but the transaction only took six weeks to negotiate. It is also not encouraging that WFM has struggled for the past few years (as seen with the awful same-store sales) and of course, does not have a technology culture.

Granted, so far, Amazon has been able to manage the complexities — and the company definitely has major advantages, such as a strong infrastructure, a powerful brand and a massive customer base. But when it comes to investing in AMZN stock, there should still be some healthy caution.

Tom Taulli runs the InvestorPlace blog IPO Playbook and operates PathwayTax.com, which provides year-round tax services. Follow him on Twitter at @ttaulli. As of this writing, he did not hold a position in any of the aforementioned securities.