It took a year without Carlos Ghosn for the auto makers he once led to realize what he had been doing for two decades: keeping Nissan Motor Co. and Renault SA from coming apart at the seams.
Since Mr. Ghosn was arrested in November 2018, insiders at the companies said the two partners, lacking a chief to impose order, have reverted to the corporate equivalent of a nasty and brutish state of nature.
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