Does Othello create his own downfall?
The fact that Othello is so easily jealous makes it easy for him to be manipulated, but does this make it his own fault? His cultural difference also does help. Plus, he trusts too readily, so he believes whatever Iago says...
No, Othello does not create his own downfall. But Iago targets Othello's vulnerabilties. Othello expresses his inadequacy in speech; he compares himself to Cassio and finds that he comes up short, he feels as if he is an outsider to Venetian society, he is not experienced with women. So, he believes Iago, as a soldier believes in his men. He finds it easier to trust the man that served under him in the field rather than the woman he has recently married. Othello falls as many do. We begin a relationship that is full of love and promise. Insecurity and jealousy creep in (symbolized by Iago), and the relationship ends with divorce and bitterness. Shakespeare understood human relationships very well, which makes this tragedy particularly poignant.
While Othello does exercise poor judgment in whom to believe (especially for an experienced military leader), I think that he--more than any other Shakespearean tragic hero--deserves less blame for his downfall. He is a product of a prejudiced society, a society which uses him for his military prowess and exotic culture but then stereotypes him as animalistic, lustful, jealous, and violent.
Iago knows that Othello is insecure in his relationship with Desdemona because of the difference in their race, age, and social class, and he uses that insecurity against the general. Thus, I think that someone could validly argue that had it not been for stereotyping, Othello might not have fallen as he did.
Many literary critics have examined the roles of responsibility in Shakespeare's Othello. Iago is the clear antagonist, and his actions certainly play a large role in eliciting such a jealous and violent response from Othello. Further, blame can be placed on Emilia, who steals Desdemona's handkerchief and doesn't own up to it, and on Desdemona, who fails to produce responses specific enough to dispute Othello's claims.
However, Aristotle defined a tragic figure as one who is plagued by hamartia--or a tragic flaw or error. It is this flaw, according to Aristotle, that brings about the tragic figure's downfall. (Further, Aristotle insists that the tragic figure is responsible for his own actions, and therefore, for his own downfall.)
Clearly, Othello is guilty of misplaced trust--he believes a man whom he didn't feel was fit for the lieutenancy over his wife, and as you note, many factors contribute to the tragedy of the play. Ultimately, though, Othello is responsible for his own actions--and is therefore at fault.