Complex sentence: By contrast, nationalisation does not necessarily imply social ownership and the restructuring of the economic system, and by itself nationalisation has nothing to do with socialism, having historically been carried out for various purposes under a wide variety of different political systems and economic systems.
Split into simpler sentences: By contrast, nationalisation does not necessarily imply social ownership and the restructuring of the economic system. By itself, nationalisation has nothing to do with socialism, having been historically carried out for various different purposes under a wide variety of different political systems and economic systems.