Which factor enabled the central ideas of the Protestant Reformation to gain acceptance throughout northern Europe?

The printing press

Explanation:

The printing press had a huge impact on the spread of the Protestant reformation because it made possible for the Protestant ideas to travel across Europe in a very fast way, also before the printing press, the Catholic Church held most of the power to produce books and after the press was invented the control was removed.

The Protestants used mostly pamphlets to spread their ideas, during that time in German, historians say that from 1500 to 1530 the Protestants had 20% more pamphlets than the Catholics.