According to The Facebook Effect, David Kirkpatrick's book about the company was founded, Facebook was a very popular M&A target.
As early as 4 months after Facebook's inception, people with money and people representing companies with money began lining up to beg Facebook cofounder and CEO Mark Zuckerberg to take their cash and sell the company.
Obviously, Zuckerberg turned all their offers down. But some offers were much more tempting than you probably realize.