In 1917, the Mother of God appeared to three children in Fatima, Portugal. She had come just a year before World War I was to end. She warned the world that a more terrible War would take place if they did not pay heed to her message. This was part of her message for July 13th 1917.
"The war is going to end. But if people do not stop offending God, another, even worse one will begin in the reign of Pius XI. When you shall see a night illuminated by an unknown light know that this is the great sign that God gives you that He is going to punish the world for its many crimes by means of war, hunger, and persecution of the Church and the Holy Father. To prevent it, I shall come to ask for the consecration of Russia to my Immaculate Heart and the Communion of reparation on the first Saturdays.
"If people attend to my requests, Russia will be converted and the world will have peace. If not, she [Russia] will scatter her errors throughout the world, provoking wars and persecutions of the Church. The good will be martyred, the Holy Father will have much to suffer, and various nations will be destroyed.
"In the end my Immaculate Heart will triumph."
In the late 1930's the Message of Divine Mercy was revealed to a simple young Polish nun just before the outbreak of World War II. Jesus was offering the world His Divine Mercy as the last hope for mankind.
Helen Kowalska (St. Maria Faustina) entered the Convent of Our Lady of Mercy in August 1925. It was during her period in this Congregation that Jesus would ask her to be the Secretary of His Divine Mercy, relating to her the Message of Divine Mercy thus preparing the world for the Second Coming. Our Lady had already warned in Fatima of another war if people did not heed her message for conversion and prayer and it was before this War began that Jesus revealed His Message of Mercy to St. Faustina for the world. World War II began when Germany invaded Poland (the home of St. Faustina and John Paul II) on Sept 1st 1939 and so began this most terrible War.
The Lord said to her: “In the Old Testament I sent prophets wielding thunderbolts to My people. Today I am sending you with My mercy to the people of the whole world. I do not want to punish aching mankind, but I desire to heal it, pressing it to My Merciful Heart.” (Diary 1588).As well, “You are the secretary of My mercy; I have chosen you for that office in this and the next life(Diary, 1605)...to make known to souls the great mercy that I have for them, and to exhort them to trust in the bottomless depth of My mercy”(Diary, 1567).