Diamondback Energy will attempt to buy rival Endeavor Energy Resources to create an energy giant in the Southwestern United States worth more than $50 billion. Growing confidence in an economic recovery, particularly in the U.S., has driven massive deals in the energy sector in recent months, including Chevron’s $53 billion acquisition of Hess in October, and a $59.5 billion deal two weeks before that by Exxon Mobil, its biggest acquisition since buying Mobil two decades ago.