1. The devil.
The Liturgy of the Mass described the steps towards salvation. First, we must know what we have done to offend God; this was taught during Shrove Tuesday. Secondly, we must know how to repent for those past sins; the Church begun to teach us this from Ash Wednesday and forward up to Easter. This consist in living a life of repentance that consist in prayer, fasting and good works.
Neither, merely, knowing one's sin nor the life of prayer, fasting and good works can forgive our past sins. Thirdly, we must attain the gift of the Holy Spirit called the fear of God.
With the 'fear of God,' the soul, also, obtains the theological virtue of Faith and Charity.
The devil who, through jealousy, wants to destroy the souls of men, knows that upon reaching Faith and Charity there is nothing he can do to destroy souls. Satan knows he has to destroy souls before the souls repents or at least when they are in the process of repentance.
Most men don't bother repenting so the devil has nothing to do to destroy them. They are, effectively, destroying their souls without any help from the devil. The devil loves to destroy those repenting, especially those who are approaching the virtues of Faith and Charity.
The devil does his dirty work through temptations.
2. God uses the devil in two ways.
The devil cannot approach or tempt any soul without the permission of God. If God ever allows the devil the approach or tempt men it is for two reasons. First, God allows the devil to tempt men with the virtue of Faith in order to help them advance in virtue and holiness.
Christ in the Gospel for today was tempted by the devil. He allowed this to show those who have Faith how to use temptations to progress in the life of virtue and holiness. St. Veronica Giuliani, John Vianney, Padre Pio were some of the saints who were accosted by devil that they may overcome the devil and advance in the spiritual life.
The second reason why God allows the devil to tempt, especially, those who have no Faith is this. Those who have no Faith are usually in the state of moral sin, that is why they have no Faith. If these sinners do not immediately repent for their past sins, their punishment from God is that God allows them to fall further into sin. And as they fall deeper into sin more devils possess their souls. So they go from worse to worse to the point that they cannot do anything good either for themselves, for their love ones, for their country or for the whole world. In fact, God punishes them by making them do evil to themselves, their love ones, to their countrymen and to the whole world. And there is nothing they can do to stop this;.....except to stop sinning, repenting and undergo the first among three conversions.
However, the deeper they commit more evil, the harder it is to repent. It is still possible but considering all matters especially that the devil will do everything to prevent them, it will be near impossible to save their souls. This is clearly seen in the much publicised lives of Catholic politicians who are pubic sinners, like those proposing abortion; everything they do after their first mortal sins is a descend to greater evil according to the moral theology of their Catholic Faith. They cannot do any thing good, they can only do evil things because this is God's punishment for them for having sinned, while refusing to repent. This is a punishment from God.
3.The world is in this descend into the bottomless pit..
Lead by the two leading figures, the Vatican and the USA, God has allowed the devil to tempt them into greater evils because both of them have sinned, the Vatican with Idolatry, the USA with abortion and with their continuous refusal to repent, God has allowed the devil to tempt them to commit more and more sin, driving them deeper into greater evil.
St. Thomas have written, he who sins against one command of Christ will sin against all the commands of Christ. One who go against one teaching of Christ goes against all the commands of Christ. Everybody seems to be at the bottom of sinfulness and possessed by legions of devils.