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You ask a great question and answers will vary. A .com is recognized and accepted well in all countries. My preference would normally be a single site with a folder for each country. By having one site, you will minimize expenses, coding and gain many efficiencies. You should use Google and Bing WMT to set your target for each section of your site. You should also ensure your country target signals are clear with language meta tags, and proper use of currencies, measurements and language. With that said, if you wanted to go from purely a ranking perspective, several credible people have shared their believe a ccTLD will outperform a .com site with all things being equal. Even if that were true, the loss of domain authority by having your sites divided, combined with other factors makes it most worthwhile to keep the sites together under the .com domain in my opinion. Opposing viewpoints are welcome