In economic theory, vertical integration involves an entity, such as a manufacturer, trying to acquire or take control of the upstream activities or downstream of the stage in which it is involved. So, a manufacturer may try to acquire some of its suppliers or the distributors or retailers it is selling to. Horizontal integration involves acquiring entities that perform a similar function either as a consolidation process or for market penetration.
A port authority is a good example of a vertically integrated structure that provides a wide array of services connecting the foreland and the hinterland. Port regionalization emerges if inland facilities such as inland (dry) ports and corridors are developed. Port holdings are attempts at horizontal integration by acquiring stakes at port terminals in various markets. A maritime shipping company that ventures into managing port terminals performs concomitantly a vertical and horizontal integration process since it is expanding geographically and from maritime towards inland services (e.g. Maersk – APM Terminals). In all cases, the outcome is a more integrated and efficient transport chain that includes maritime shipping, port terminal operations, inland access, and even freight distribution centers (as a 3PL service to customers). Port regionalization is emergent if inland facilities such as inland (dry) ports and corridors develop.