When someone is freed from an unclean spirit, seven other spirits more wicked than the first one can return to the person, if he opens the door to demons through his unrepented sins.
Pope John Paul II has called for a "new evangelization." By this, he means the evangelization of nations and cultures which were formerly Christian but have lost the faith. When these nations were evangelized, millions of people received new life in Jesus and were freed from unclean spirits. Now that these nations have lost their faith, seven times more demons and far worse demons have the opportunity to re-possess these cultures fallen away from the faith (Lk 11:26). This means the Western culture, including the United States, may be packed with demons.
Because demons are masters of deceit, they can disguise their presence. So it is difficult to determine the degree of demonic presence. However, we can get some idea about how many demons are active by looking at death, slavery, and fear, for these are areas in which demons specialize (Heb 2:14-15). Pope John Paul II has described this culture as a "culture of death." Many are enslaved through addictions and compulsions. Fear abounds — from fear of terrorism to fear of biochemical warfare to phobias. Therefore, we have reason to surmise that there is a very thick demonic concentration where we live. We need not be afraid, but we must keep our hands in the hands of Jesus.