Source: Facebook

Shares of Facebook (NASDAQ:FB) fell as much as 20% in August, after a series of economic events in China affected the international markets. Tech companies were some of the hardest hit by the downturn.

The biggest factor affecting businesses without significant operations in China (such as Facebook) is the recent devaluation of the Chinese yuan, which the government let fall 3% to 4% in relation to the U.S. dollar. Considering the amount of U.S. debt China holds, this creates a stronger U.S. dollar in every market. As a result, any company that does business internationally but reports earnings in U.S. dollars will feel the impact on their income statements.

But Facebook does nearly half of its business in the United States
Through the first six months of 2015, the United States and Canada accounted for about 49% of Facebook's total revenue. And while the Canadian dollar just hit an 11-year low against the U.S. dollar, it's a relatively safe assumption that most of that revenue is U.S.-based already.

In other words, the strong dollar won't have a huge impact on about half of Facebook's revenue.

What's more, Facebook's revenue in the U.S. and Canada is growing faster than any other region. Last quarter, the company increased revenue in the U.S. and Canada 50% year over year. While the Asia-Pacific region grew 45%, most of that growth was driven by user growth.

Asia-Pacific is still seeing significant user growth, increasing 21% year over year last quarter. Comparatively, the user base in the U.S. and Canada grew by just 4%. In other words, Facebook is still mostly focused on growing out its user base in the region, as opposed to increasing monetization. The opposite is true in the saturated U.S. and Canada market.

The different strategies are evident in the company's average revenue per user results. ARPU increased nearly 50% in the U.S. and Canada last quarter. Comparatively, Asia-Pacific was more in line with the ARPU growth in Europe, coming in at 19% year over year. Certainly, some of this performance was affected by the already strengthening dollar over the past year, but the growth disparity is much bigger than that, indicating a strategic difference in the regions.

Asia-Pacific still accounts for a tiny portion of revenue
More importantly, the percentage of revenue coming from Asia-Pacific is still just about 15%. Asian currencies were the hardest hit by the economic events in China, so investors can expect it to have an impact on Facebook's revenue from the region. But that impact will be small in relation to Facebook's total revenue.

Additionally, the small percentage of revenue that comes from Asia indicates that Facebook can still grow its revenue in the region despite currency headwinds. As mentioned, most of Facebook's revenue growth is driven by increasing its user base. With the Internet populations of India, Indonesia, Taiwan, and other South Asian countries expanding rapidly, Facebook has plenty of room to expand its revenue by growing its user base.

The sell-off is an opportunity
With Facebook's huge concentration of revenue in the United States, a strengthening dollar isn't as big of a concern for the company as it is for other large international tech companies. While it will have an impact on its revenue from other regions, the biggest impact will be in a region where it produces just 15% of its revenue. As a result, the earnings hit from foreign exchange headwinds should be minimal.

Since a stock's price is supposed to represent the underlying value of the company's future earnings, Facebook's stock seems to have gotten caught up in the momentum of the market. Analysts' expected earnings for Facebook have gone up across the board over the past 30 days. As a result, Facebook is trading at a relatively low forward P/E ratio, making it look like an excellent time to buy.