Macbeth is a classic example of a tragic hero. His own character flaws ultimately lead to his downfall. That's the important thing here - there are certainly some examples of Macbeth being a victim of circumstance, but he ultimately did himself in with his greed and ambition. These traits were inherently his. Circumstances may have influenced him greatly, but they did not make him greedy and ambitious.
Examples of being a victim of circumstance:
1. The prophecy of the three witches
In Act I, Scene III Macbeth and Banquo encounter three witches who make some very intriguing claims. They tell Macbeth that he will be king. This idea immediately fills his head with wonderment and ambition. He's clearly excited about this notion, but it's also obvious that he's not sure how to act on it, or if he will even act on it at all. We see his internal struggle with his natural ambition and greed against his thoughts of kindness and honor. Had he never encountered these witches and heard their prophecy, he may never have thought of striving to be king of Scotland.
2. Lady Macbeth's ambition and influence on Macbeth
Macbeth's ambition is only outdone by his own wife's ambition and greed. She desires the finest things and the highest status. When she learns of the prophecy, she immediately begins working on manipulating her husband. It is her idea to kill King Duncan and she wastes no time in pressing this idea on Macbeth. When he hesisates at the idea, she responds by mocking him and questioning his manhood. "When you durst to do it, then you were a man" (Act I, Scene VII). Lady Macbeth goes to the lengths of concocting the entire plan to kill Duncan, even how to cover their tracks. She manipulates and nags her husband until he reluctantly agrees to carry out the evil deed. Without Lady Macbeth's influence, would Macbeth have murdered Duncan? You could argue that he would not have since he was very uneasy about the idea in the first place and repeatedly tried to back out of it.
3. Macbeth himself
We've established that Macbeth had certain inherent qualities - he was greedy and ambitious. Could he control those urges within himself or was he predisposed to be that way? We saw what happened once a seed was planted in his head (that he'd be king). He killed Duncan, killed his best friend Banquo, killed the family of another friend, and turned his entire country against him. His greed and ambition turned to stubborness and he died because of it.