Linked from
The 51 pages that link to Group, each with the reason it gives.
Group theoryBroader topic: This algebraic structure is the basic object group theory studies.
AssociativityBroader topic: Associativity is one of the defining group laws.
Associative propertyBroader topic: Associativity is one of the defining group axioms.
MagmaBroader topic: A group is a much more constrained structure built around a binary operation.