During the earlier years of the school bus industry, the factory manufactured most of the parts used to assemble a bus body, but it was customary for these to be shipped unassembled to body dealers around the United States and Canada, for assembly onto an incomplete truck chassis. Gradually, as highway transportation of completed buses became more practical, and school bus bodies became more sophisticated; the assembly of complete bodies onto truck chassis in the United States and Canada became centralized at locations owned by the body companies. The companies often continued to ship "kits" overseas.