Shareholders of Nipponkoa Insurance Co. on Wednesday approved a merger with Sompo Japan Insurance Inc., paving the way for the two companies to form Japan's third-largest nonlife insurance group.

The endorsement by shareholders followed an announcement by the insurer's largest stakeholder, U.S. investment company Southeastern Asset Management Inc., that it supports the merger. Its support paved the way for Nipponkoa to obtain the two-thirds majority required for approval.