Nissan and Honda ended merger talks to forge a $60 billion car company on Thursday, pitching Nissan deeper into uncertainty and highlighting the pressure on legacy automakers from Chinese rivals upending the industry.

Although Mitsubishi considered joining the Honda-Nissan merger, that was old news by late January. That alliance might have been part of the problem. Although not an actual merger, the car companies involved each own stakes in the other—in Renault's case,