Delta Air Lines has spent $2 billion over the last five years investing in foreign airlines, pinning its global strategy on building a vast network that extends far beyond the routes flown by its own aircraft. A transpacific joint venture (JV) with Korean Air, already approved by U.S. regulators and awaiting clearance from South Korea’s government, will become Delta’s seventh cross-border tie-up that involves an antitrust-immunized JV or an equity stake, or both. Nowhere is this ...