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

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 American Tower (NYSE: AMT). We'll examine not only where its sales and earnings come from, but also how its sales abroad have changed over time.

Where American Tower's assets were five years ago
Since American Tower didn't report foreign sales five years ago, we can get a good proxy on its previous international exposure by looking at its assets during that time. The company owns towers that it leases to mobile companies, so its assets correspond closely to the regions where the company is seeing sales.

Source: S&P Capital IQ.

Where American Tower's assets are today
Today, 81% of American Tower's assets are still held in the United States, but it's rapidly expanding internationally. 

Region

2008 Assets

2010 Assets

United States 6,339.9 6,565.9
Mexico 327.4 215.1
Brazil 98.5 242.9
Chile -- 25.7
Colombia -- 162.6
India 9.2 807.6
Peru -- 79.6

Source: S&P Capital IQ.

Since 2008, almost all of American Tower's growth has been into new Latin American markets and India. It's common to read stories about the company's Indian opportunity, but seeing its asset growth in the country underlines the commitment American Tower is making to finding growth on the subcontinent.

Competitor checkup
One last point to check is how American Tower's footprint compares with some of its peers and industry rivals:

Company

Geography With Most Sales

Percent of Sales

American Tower United States 73%
Crown Castle (NYSE: CCI) United States 94%

Source: S&P Capital IQ.

Of its closest peers, American Tower has the strongest geographic reach. Crown Castle maintains a strong presence in Australia, but it's still dwarfed by the company's American operations. SBA Communications (Nasdaq: SBAC) doesn't report sales by region, but the vast majority of its towers are in America. The company also has site leasing business in Canada, Costa Rica, El Salvador, and Panama, but it plans further expansion internationally through builds and acquisitions.

Keep searching
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Eric Bleeker owns shares of no companies listed above. You can follow him on Twitter to see all of his technology and market commentary. Motley Fool newsletter services have recommended buying shares of American Tower. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.