Which 2010 airline merger created what was then the world's largest carrier by passenger traffic, fundamentally changing the competitive landscape of the US aviation industry?

The airline industry has seen numerous mergers and acquisitions over the decades, reshaping the competitive landscape of global air travel. One particular merger stands out as a game-changer that created what was, at the time, the world's largest airline. Test your knowledge of transportation industry history with this trivia question about a transformative airline merger that significantly impacted the aviation sector and set off a wave of consolidation in the industry.

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United Airlines and Continental Airlines
Delta Air Lines and Northwest Airlines
American Airlines and US Airways
Southwest Airlines and AirTran Airways