In today's world, most companies span several regions and sell around the world. As Foolish colleague Morgan Housel notes, 10 years ago, less than a third of S&P 500 revenue growth came from abroad. Today, that area makes up half of the S&P 500's growth.

And that number is growing. The truth is, investors regularly underestimate how much demand comes from abroad. More importantly, for large, multinational corporations that have already established a presence in their home markets, much of their future growth comes from abroad.

With that in mind, today we're looking at Citigroup (NYSE: C). We'll examine not only where its sales and earnings come from, but also how its sales abroad have changed over time.

Where Citi's sales were three years ago
Three years ago, Citi produced 35% of its sales within North America.  

Source: S&P Capital IQ.

Where Citi's sales are today
Today, as the rest of its large corporate peers see the influence of foreign sales rise, Citi's situation is little changed.

Source: S&P Capital IQ.

Citigroup counts 37% of its sales from North America, good enough to make it the most geographically diversified of the larger American banks. That could give pause to investors who are looking to avoid the so-called "PIIGS" of Europe, but there doesn't appear to be a huge difference between Citi's assets in the country's and the level of assets held by other U.S. banks like Bank of America (NYSE: BAC).

As a small example of the company's global influence, Citigroup recently became the first Western bank to receive regulatory approval to issue credit cards under its own name in China. While China will always be a stubbornly difficult environment for foreign financial firms, Citi is positioned for greater growth across Asia.

Banking can be more complex in other countries, especially with financial liberalization facing a long slog in the booming Chinese market, but there's no way to avoid the key point that markets like Asia and Latin America will become increasingly important in the financial world across the following decades. With high savings rates and growing middle classes, growth could first come to areas like asset management and flow into higher-margin trading segments. In any case, Citi's global position could leave it as a great long-term play on a bullish economic prospects across the world.

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