It was not the witches or Lady Macbeth but his own vaulting ambition that was responsible for Macbeths descent into darkness.
Macbeths descent into darkness was not wholly his fault. There were other factors that contributed to his descent. The Witches and Lady Macbeth were also partly responsible. It is unfair to place all the blame on Macbeth even though he made all the choices and committed all of the crimes himself.
The play opens with witches plotting to destroy Macbeths life. So even at the very beginning of the story it is clear that the Witches will have a terrible influence on Macbeths future. They tell Macbeth of three predictions. All hail, Macbeth! Hail to thee, Thane of Glamis. All hail, Macbeth! Hail to thee, Thane of Cawdor! All hail, Macbeth, that shalt be king hereafter. (The Witches) Now obviously at least the first and second of the predictions are true because immediately after Macbeth hears them he is awarded the title of Thane of Cawdor. However the witches may have known about the second set of predictions from the very beginning, which are the predictions that result in Macbeths downfall, in which case they knew that if Macbeth was not aware he would become king it may have never happened at all. If Macbeth didnt know about the prophecy he wouldnt have written the letter to Lady Macbeth explaining what had happened, and she wouldnt have convinced him to kill King Duncan, so he could become King himself and her Queen. If Macbeth and Lady Macbeth had have waited patiently Macbeth may have become King innocently in later years and the second prophecy would not have occurred. So either the Witches caused the second set of predictions to happen, by telling Macbeth first, or they knew about the second set all along, so if they hadnt have told him he wouldnt have become King and had his life destroyed. The Witches also deliberately left out crucial details of the predictions to make it sound as though Macbeth was going to be successful.
Lady Macbeth was also largely responsible for Macbeths descent into darkness. When she received the letter from Macbeth about the prophecy she wanted to immediately become Queen. She gained such ambition that she convinced Macbeth to kill King Duncan to become king. She attacked his manhood until he gave into her demands. and live like a coward in thine own esteem. Letting I dare not wait upon I would. When you durst do it, then you were a man. (Lady Macbeth to Macbeth) She could have killed King Duncan herself but she didnt. She was contradicting herself; being exactly what she was accusing Macbeth of being. She only saw hers and Macbeths future as king and queen. She didnt see the consequences of their actions, the guilt they would be feeling afterwards, and what would soon become a domino effect. If she had have spent more time thinking about the predictions she would have realised that they were inevitable, and would have been patient and waited for the time to come. She may have even come to the conclusion that it was best to leave it all alone as nothing good can come from something bad.
Macbeth is the other person responsible for his descent. He had his doubts about the witches from the very beginning. This supernatural soliciting cannot be ill; cannot be good. If ill why hath it given me earnest of success commencing in a truth? (Macbeth referring to the Witches) Macbeth could have easily chosen to have nothing more to do with them but instead he chose to dote on it and in doing so he told Lady Macbeth. Lady Macbeth badgered Macbeth until he did what she told him to do. If he had been a stronger person he would have been able to stand up to her. He made the choice to listen to his wife and kill King Duncan when his conscious told him not to. He knew it was the wrong thing to do. He was a full-grown man able to say no to whatever he wanted to. He didnt have to let people influence his decisions. It was his own weakness that let him be pushed into a world he didnt have to live in. Then his ambition began to grow as soon as he became king. For everything he did wrong, he had to do more wrong to cover it up and before he knew it he had basically dug his own grave.
There were many things that contributed to Macbeths descent into darkness. The blame cannot be placed on only Macbeth even though he was the person who acted out all of the things that turned him into the horrible person he became. The witches tricked him. They deliberately manipulated him, and they had the power to do that. He was let down by his own wife. If she loved him she would have been patient and not forced him to do something he didnt want to do and something she didnt have to courage to do herself. It is true that Macbeth could have been smarter and not let himself be manipulated the way he was, but there was an enormous amount of pressure on him that people in the world today dont normally have to deal with, especially in that sort of situation.