The Lady forecasted a worse war than World War One during the reign of Pius XI if Russia was not consecrated to her and that God would send it to punish the world (Is this the Third Secret? page 5). The Second World War did not happen during the reign of Pius XI but Pius XII.
The worse war that started under Pius XI was of Communism against Christianity. World War Two was a kind of pause or distraction in it. First main battles were Communist régime of Mexico provoking Cristero rising and executing capitulating insurrectionists, then the War in Spain. 1938, Hitler crushing Catholic Austria was part of that war too.
After WW-2, except in US, victors were as often as not attacking Catholic Church. There are more things to be said. Here is the site I am answering:
BBL, I suppose./HGL