The Book of Genesis is adamant that humans caused evil and that God is not to blame. In the beginning, Genesis 1, God create a world and saw that it was good. He then created humans and left them in an idyllic place, but human disobeyed and lost the idyll. Curses fell onto the whole human race because of the sin of a representative ancestor. But this view struggles with the realization that Adam and Eve are mythical figures, so the tale is not literally true. Furthermore, it makes God appear quite unfair. I don't expect to suffer for my great, great grandfather's moral faults, so why should I have to suffer for Adam?
Augustine in the fifth century developed the Adam and Eve tale and ran with it. Humans were all born into sin inherited through sexual relationships from Adam, so all were doomed to Hell. But from Adam they inherited conscupiscence, a disorder in human nature that makes for excess, which explains human propensity for sin. However, some were predestined to be saved by Christ, through the cross. Tough on the rest.What this cruel image of God has to do with the loving Father of Jesus Christ went unspoken, but it says much about the critical thought of the clerics who have for centuries slavishly followed Augustine for centuries.
Yet Augustine's was not the only Christian theory. Irenaeus, bishop of Lyons, argued that the world was the vale of soulmaking, a place where humans learned to improve, so it was inevitable that during the learning process mistakes would be made. This is a theory more humane and fair to God than Augustine's, but it was inexplicably the less popular of the two.
Origen, a controversial figure of the third century, took another view of evil. Humans lived in a cyclic world, having various incarnations. Some souls fell from the higher spiritual levels out of love for pleasure. They then became human and were prone to evil. However, through spiritual development they can rise up the spiritual ladder and become pure. Even Satan would be eventually saved. Theology has had a love-hate relationship with Origen, All theologians know his scholarship, but they reject his unorthodoxy. I have even known an evangelical scholar describe him as a pagan thinker: a total injustice to a Christian who suffered horrendous tortures for his faith, but that's what you get if you disagree with a narrow minded theologian! Origen is interesting in that as an Egyptian he may have been in contact with Indian thought, which may have influenced his views. There are certainly influences from the Greek philosophy or Orphism, which shared Hindu views on a cyclic world.
Pelagius, Augustine's bete noire, whom Augustine had driven out and exiled [nice man wasn't he] argued that Adam's sin worked not by inheritance but by example. Quite a modern theory of the origins of evil. But this was not taken up by the church as an ultimate explanation.
The Christian belief is that humans caused the problems in the world, eagerly aided by Satan. But this begs a question, why does God simply not stop us sinning? Here is where theology moves forward.