Varignon's Theorem:

This states that the moment of a force around any point is equal to the sum of the moments of its components around the same point. This principle is also called as principle of moments.

Varignon's theorem need not be limited to the case of just two components but equally applies to a system of forces and its resultant. For this, it may be slightly changed like, "the algebraic addition of the moments of a given system of forces w.r.t. a point is equal to the moment of their resultant around the similar point". This principle of moment might be extended to any force system.