After an incredible run, investors finally got a reminder in 2018 that stocks really don't just go up. From 2009 through 2017, they enjoyed a nearly unprecedented string of positive years, with both the S&P 500 (^GSPC -1.34%) and Dow Jones Industrial Average (^DJI 0.50%) delivering positive total returns every single year.

That streak may have come to an end in 2018, but individual investors should continue to look to stocks as the best way to build wealth over the long term. After all, the global economy is only going to get bigger, and more of the world's population is set to join the middle class in the decades to come.

Case in point: The global middle class is expected to grow by an incredible 1 billion people in less than 20 years. It's going to take a big boost in infrastructure to support their needs, while their added wealth and spending will help create a more vibrant global economy. This isn't a zero-sum game: These new middle-class consumers will be a rising tide that lifts all boats. 

Using tiny tools to plant money.

These two stocks could grow your money substantially over the long term. Image source: Getty Images.

Two companies set to prosper from a more vibrant, wealthier, and tech-driven global consumer class are NV5 Global (NVEE -0.50%) and Axos Financial (AX 0.47%). With strong leadership, solid financial footing, and incredible runways for years of growth, these companies could deliver truly life-changing wealth for investors over the next couple of decades. 

Check out the latest NV5 Global and Axos Financial earnings call transcripts.

The massive infrastructure opportunity

This isn't news to anyone who's driven on a road or seen the coverage of the Flint, Michigan, water system: America's infrastructure is old, outdated, and -- in many cases -- in extreme disrepair. According to the American Society of Civil Engineers, the U.S. needs to spend $4.6 trillion over the next decade just to bring it up to snuff. On a global basis, most of the middle-class expansion is going to take place in high-growth urban environments. Estimates top $90 trillion to build out the transportation, utility, and telecommunications infrastructure that these future populations will need. 

Furthermore, these projects are rarely simple and straightforward, often requiring engineers from multiple disciplines to design and plan them, construction companies with multiple specialties to build them, and an army of project managers to coordinate it all. NV5 Global is taking full advantage of this major global need to deliver all of the engineering, consulting, and project managing services it takes to move an infrastructure project from planning to putting into operation. 

Since going public in late 2013, NV5 has grown substantially. Revenues are up almost 500%, while earnings per share have increased 226%. Investors have enjoyed 773% gains since its IPO:

NVEE Chart

NVEE data by YCharts

And I think the best is yet to come. NV5 is still very small, compared with some of the biggest engineering and construction companies:

NVEE Revenue (TTM) Chart

NVEE Revenue (TTM) data by YCharts.

Yet as much as there are some very big players, the industry is also ripe for consolidation, with some 100,000 separate engineering companies operating in the U.S. alone. NV5 management has proven incredibly skilled at finding the best of these to acquire and integrate, turning more of the revenue the company earns into profits, while delivering a better potential product and easier-to-manage project for customers. 

With a market cap of less than $900 million, and trading for 17 times estimates for 2019 earnings per share, NV5 is both cheap and tiny. With incredible management and a huge market opportunity, it's one of the best growth stocks I've found in years. 

The future of banking is here

Over the past decade, people's relationship with their bank has changed significantly. Gone are the days when visiting a bank branch was a necessary part of life for millions of Americans, and no single entity is better proof of that than Axos Financial. Since going public as BofI Holding and operating as Bank of the Internet, Axos has grown profits an incredible 4,600% and delivered almost 850% in total returns without operating a single publicly accessible retail location:

AX Chart

AX data by YCharts

Yet just as NV5 remains a small fish in the infrastructure pond, Axos is a tiny minnow in the banking ocean. Here's how it compares in total assets with the biggest banks:

AX Total Assets (Quarterly) Chart

AX Total Assets (Quarterly) data by YCharts.

That's not to say that I expect Axos to become the next JPMorgan Chase. It's meant to highlight that at around $10 billion in assets, Axos is still a very small bank. But its branchless model gives it a substantial leg up in terms of turning more of every dollar in interest it gets into earnings on the bottom line. And CEO Greg Garrabrants has proven as skilled as any banking executive at allocating those profits into building a bigger, more-profitable bank. 

Furthermore, Axos stock, like many bank stocks, has taken a bit of a beating as investors worry over a potential economic slowdown taking a bite out of profits. Economic uncertainty could turn into a recession at some point (hint: eventually it will). But this short-term thinking -- because every recession ends and the economy ends up stronger on the other side -- has created an excellent buying opportunity for this small, high-growth bank. 

At recent prices, Axos shares trade for 11 times 2018 earnings. This isn't just cheap: It's cheaper than big banks like JPMorgan with far smaller growth prospects, and even Wells Fargo, which isn't even allowed to grow right now. Axos, on the other hand, should be able to continue delivering double-digit asset and earnings growth for many years. Those who take advantage of the current bargain-bin price could see their investment become substantially larger in the years to come.