Long before CaroTrans, there was Carolina Freight.  It was a gigantic, predominantly domestic trucking operation in the US that was established in 1932.  By the mid 80's Mainfreight had established a relationship with them, operating as their agent in New Zealand.

In 1989, Mainfreight was able to head to the US to tour Carolina Freight and quickly realized the many similarities between the companies.  Mainfreight even gained access to their systems and were so impressed they went back home and began using similar technology to help them advance how they move, track and trace freight.
Unbeknownst to many, Carolina Freight had two international groups, one of which was their international freight forwarding business, CaroTrans.  It was created in 1979 by Jim Justiss of the Carolina Freight group.  By the mid-90's Carolina Freight was struggling to survive and it was during this time they decided to combine the international divisions in an effort to protect that part of the business.  
Ultimately by 1996, Carolina Freight was purchased by Arkansas Best Corporation who inherited CaroTrans in the deal.  They were not looking to take over an international division and decided they would sell this piece of the business.

Mainfreight already had an agency agreement in place with CaroTrans from their Carolina Freight relationship.  And with CaroTrans up for sale, they knew they didn't want it to be sold to a competitor.  It was then, in March of 2000, Mainfreight decided to purchase a 50% stake in the company.  By early 2003 they purchased the remainder of it making CaroTrans a full part of the Mainfreight group.