What is the proof of the parallel axis theorem?

The proof of the parallel axis theorem involves using the moment of inertia formula and the distance between two axes. By applying the formula and considering the distance between the axes, it can be shown that the moment of inertia of an object about a parallel axis is equal to the sum of the moment of inertia about the object's center of mass and the product of the object's mass and the square of the distance between the two axes.