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A personal union is a combination of two or more states that have the same monarch while their boundaries, laws, and interests remain distinct.A real union, by contrast, involves the constituent states being to some extent interlinked, such as by sharing some limited governmental institutions. Unlike a personal union, in a federation or a unitary state, a central (federal) government spanning all member states exists, with the degree of self-governance distinguishing the two. The ruler in a personal union does not need to be a hereditary monarch.