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Advertising and expanding around the globe would be a good place to start. It's not cheap to find/put top-notch staff on the other side of the world to expand a business, open offices, recruit drivers and customers, etc.

Acquisitions? Lobbying?

An acquaintance started a mapping company, and Uber snatched it up almost overnight. Although I expect a lot was paid in stock, which isn't included in these losses.

It is very different from country to country how they do stuff. When they where in China they heavily subsidized rides, paying drives more than the entire fare, sometimes.