1 The race of man, after its miserable fall from God, the Creator and the Giver of heavenly gifts, "through the envy of the devil," separated into two diverse and opposite parts, of which the one steadfastly contends for truth and virtue, the other of those things which are contrary to virtue and to truth. The one is the kingdom of God on earth, namely, the true Church of Jesus Christ; and those who desire from their heart to be united with it, so as to gain salvation, must of necessity serve God and His only-begotten Son with their whole mind and with an entire will. The other is the kingdom of Satan, in whose possession and control are all whosoever follow the fatal example of their leader and of our first parents, those who refuse to obey the divine and eternal law, and who have many aims of their own in contempt of God, and many aims also against God.
Source: Humanum Genus (Vatican.va)