Following a period of historic stock market volatility, long-term investors have once again learned the value of being patient. Since the widely followed S&P 500 hit bottom during the coronavirus pandemic, the index has catapulted higher by 95%.

However, investors should also be aware that bounce backs from bear market lows are never this smooth. Multiple aspects of history are working against equities in the near term and suggest that turbulence might arise. Rather than putting your money to work in individual stocks, this might be the perfect time to put the diversification of exchange-traded funds (ETFs) to work in your portfolio.

An ETF is a security that trades like a stock but holds stakes in dozens or hundreds of companies with a specific focus. If you want to focus on companies of a certain size, growth, or value -- or a particular industry or sector -- there's undoubtedly an ETF for that.

As we head into the second half of 2021, the following trio of exchange-traded funds have the potential to make investors a lot richer.

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Global X Cybersecurity ETF

Though there are a number of high-growth industries that could perform well in the second half of 2021, there may not be a safer fast-paced trend than cybersecurity. That's why investors should consider buying the Global X Cybersecurity ETF (NASDAQ:BUG).

Long before the coronavirus pandemic struck, businesses of all sizes were beginning to shift online and move their data into the cloud. But the pandemic dramatically accelerated this shift, pushing a lot of enterprise and consumer data into the cloud and placing the onus of protecting this information on third-party providers. No matter the size of a business or the state of the U.S./global economy, cybersecurity has become a basic-need service that businesses will spend big bucks on.

The Global X Cybersecurity ETF has about $552 million in net assets and stakes in 32 cybersecurity stocks. Although many of these companies aren't cheap, you're paying a premium for the sustained double-digit growth of the industry. 

The reason I chose the Global X Cybersecurity ETF is simple: It highlights some of what I believe to be the best authentication players in the industry. CrowdStrike Holdings (NASDAQ:CRWD) is currently the largest holding at 7.1% of net assets. CrowdStrike's cloud-native Falcon platform relies on artificial intelligence to grow smarter over time and has been overseeing 6 trillion events on a weekly basis. In just a four-year stretch, CrowdStrike has seen the percentage of its customers that purchased at least four cloud-module subscriptions skyrocket from 9% to 64%. 

Okta (NASDAQ:OKTA) happens to be the fifth-largest holding. The company is a leader in identity-verification solutions that, like CrowdStrike, leans on machine learning, which allows its cloud-based solutions to quickly identity and respond to potential threats. Okta also recently closed on its acquisition of Auth0, which should help the company push into Europe.

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Vanguard Utilities Index Fund ETF

Another smart way to get richer in the second half of 2021 is to consider putting your money to work in the Vanguard Utilities Index Fund ETF (NYSEMKT:VPU). As its name implies, this ETF very closely tracks the performance of a utility index.

Despite growth stocks leading the charge, the safety and predictability of utility stocks might come in handy as a hedge in the second half of 2021. There are a number of reasons to believe that a stock market crash or correction is coming, and recent economic data demonstrates that inflation has begun rising. This should move companies that generate steady cash flow and higher dividend yields, such as utilities, into focus.

The Vanguard Utilities Index Fund ETF has approximately $4.7 billion in net assets, holds stakes in 65 companies, and most importantly has a net expense ratio of a mere 0.1%. This net expense ratio describes the total fees you'll pay to own a stake in the Vanguard Utilities ETF. A 0.1% expense ratio works out to just a fraction of the 3.1% yield you'll net from this exchange-traded fund. 

Not surprisingly, America's largest utility by market cap, NextEra Energy (NYSE:NEE), is leading the charge (13.63% of net assets). NextEra is unlike most utilities in that it's been investing heavily in renewable-energy projects for a long time.

No other utility generates more capacity from solar or wind, and NextEra has devoted between $50 billion and $55 billion to these cleaner-energy projects between 2020 and 2022. The ability to lower its electric-generation costs is allowing the company to grow at a sustainable high-single-digit percentage in a sector known for low-single-digit growth.

Sporting an annual average return of 9.7% since its inception in 2004, the Vanguard Utilities ETF looks to be a steady breadwinner for investors.

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AdvisorShares Pure U.S. Cannabis ETF

A third exchange-traded fund that can make investors richer in the second half of 2021 and likely well beyond is the AdvisorShares Pure U.S. Cannabis ETF (NYSEMKT:MSOS).

Pretty much no one disputes that cannabis sales are rising around the world. But there's a big difference between the U.S. pot market and other cannabis markets. Although BDSA is forecasting a more than doubling in Canadian weed sales to $6.4 billion by 2026, the Canadian marijuana market has been hammered by regulatory issues, supply chain bottlenecks, and value-seeking consumers.

In other words, the U.S. and its more than $41 billion in expected weed sales by 2025, according to New Frontier Data, is in a class of its own. That's why focusing on the U.S. cannabis market makes so much sense.

Another thing to realize about investing in U.S. marijuana stocks is the market doesn't need federal reform to thrive. Thus far, 36 states have legalized medical marijuana, with another 18 waving the green flag on adult-use consumption.

The AdvisorShares Pure U.S. Cannabis ETF has just shy of $1 billion in net assets and currently holds stakes in 30 marijuana stocks, most of which are multistate operators. Most notably, it has nearly 11% of its assets tied up in Trulieve Cannabis (OTC:TCNNF).

Instead of launching a presence in as many legalized markets as possible, Trulieve Cannabis has opened 85 of its 91 operational dispensaries in Florida. Saturating the medical marijuana-legal Sunshine State has kept its marketing budget down and pushed the company to 13 consecutive profitable quarters

The largest fund holding (12.9% of net assets) is Green Thumb Industries (OTC:GTBIF), which has well over 50 operational dispensaries. Green Thumb has targeted states where retail-license issuance is limited in order to ensure that it secures a healthy share of billion-dollar markets. It's also not been afraid to buy its way into lucrative markets, as evidenced by the Integral Associates acquisition in Nevada back in 2019.

Pardon the blatant pun, but the AdvisorShares Pure U.S. Cannabis ETF should have investors seeing green.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.