The fundamental cause that brought the Thirty Years' War to a close was
mental insight into the uselessness and hopelessness of further
struggle, caused by the feeling of exhaustion due to the long
continuance of the war. The reason why this war put an end to all
religious wars was, that this intellectual insight became general in
Europe, inculcating more liberal religious views. This psychological
attitude, with increasing indifference to religion and resultant
skepticism, caused religious questions to be regarded less seriously,
making further wars for such purposes impossible. The basal reason,
therefore, was the intellectual realization of the foolishness of
bloodshed on account of difference of religious convictions; that is,
lack of knowledge of this fact in the past--in short, ignorance--was at
the bottom of it all, as of most evils in the world.