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Even though August turned out to be a rough month for all bank stocks, as well as the stock market in general, some banks fared better than others. Among banks with roughly $50 billion or more in assets, three in particular stood out: Fifth Third Bancorp (NASDAQ:FITB), Zions Bancorporation (NASDAQ:ZION), and U.S. Bancorp (NYSE:USB).

BANK

August Performance

Fifth Third Bancorp

-5.48%

Zions Bancorporation

-5.97%

U.S. Bancorp

-6.06%

New York Community Bancorp

-6.31%

JPMorgan Chase

-6.46%

State Street

-6.83%

KeyCorp

-6.85%

PNC Financial

-6.85%

Regions Financial

-7.52%

Goldman Sachs

-7.86%

Wells Fargo

-7.91%

Bank of America

-8.05%

SunTrust Banks

-8.27%

Bank of New York Mellon

-8.29%

BB&T

-8.43%

Citigroup

-8.49%

Morgan Stanley

-11.12%

Source: YCharts.com

Fears about an economic slowdown in China have been blamed for causing stocks to fall. Yesterday, officials in the East Asian country reduced their estimate of China's growth rate in 2014 down to 7.3% from 7.4%. And today brought more bad news. A new report showed that exports from the country fell last month by 5.5% from the previous year and its imports were down by 13.8%.

All of this is particularly disturbing given that China's rapid growth rate has helped the global economy expand in the aftermath of the financial crisis. With Europe ever-teetering on the brink of recession and growth in the United States continuing to lag its long-run potential, China has been the global economy's shining star. But all of this came to a screeching halt when the country decided to devalue its currency in the second week of August. The news sent shockwaves through the market, leading at one point to a more than 1,000-point single-day drop in the Dow Jones Industrial Average -- though the widely followed index later made up some of the difference.

There are two concerns when it comes to banks. The first is whether a bank has direct exposure to China, which could be affected if its economy does in fact go into a tailspin. This is presumably why global banking powerhouses like Citigroup and Morgan Stanley suffered the most last month, with their shares falling by 8.5% and 11.1%, respectively. This is also presumably why Fifth Third Bancorp, Zions Bancorporation, and U.S. Bancorp were the industry's best performers, as their businesses are focused almost exclusively in the United States.

Along these same lines, the second concern is that the news from China will cause the Federal Reserve to wait even longer before raising interest rates. Increasing them now would boost the value of the dollar relative to the yuan. It would also make borrowing more expensive and thus weigh on loan demand. All of these issues are bad for economic prospects in the United States.

The downside to not raising rates, however, is that banks will continue to make less money from their loan portfolios. This is particularly true for regional lenders like Fifth Third Bancorp, Zions Bancorporation, and U.S. Bancorp, who get the majority of their revenue from net interest income and thus have the most to gain from rising rates.

It's impossible to say how all of this will eventually play out, but it's worth noting that bank stocks are cheaper today than they're likely to be in the future. Once rates do in fact rise, banks will make more money and their share prices will respond in kind. Consequently, if you're interested in adding bank stocks to your portfolio at some point over the foreseeable future, it would probably behoove you to do so sooner rather than later.

John Maxfield has no position in any stocks mentioned. The Motley Fool owns and recommends Wells Fargo, and recommends Bank of America. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.