In many Hollywood movies set in the Middle East (and particularly those set on the Arabian peninsula, Egypt, and in former Persian countries), the scores always feature a very certain 'type' of music, for lack of a better word. You can hear it in everything from Iron Man 3 to The Mummy to Harry Gregson-William's Prince of Persia theme. I have a couple of questions about this: what style of music are Hollywood composers generally patterning their music on when they do this, when did it become the ubiquitous signal for 'Middle East' in Hollywood films regardless of the country being portrayed, and why/how (besides lack of originality and a convenient musical cue to signal 'hey we're in the Middle East now') did this particular type of music get chosen for that purpose?
This is a terrific example of semiotics in music; that is, the use of signs and signifiers to evoke certain places, time periods, actions, behaviors, character types, emotions, etc. In this particular case (movies referencing the Middle East), the composers are making use of tone-colors, pitch collections, motivic gestures and other features (generally referred to as "topics" in semiotic parlance) that are common to or stereotypical of actual Middle Eastern music in order to evoke that setting.
For signifying Middle Eastern music in particular, harmonic minor scales are probably the most immediately recognizable topic, especially when focused on the augmented second interval between the sixth and raised seventh scale degrees in the upper tetrachord. There is a long history of this kind of Middle Eastern and Eastern exoticism in Western classical/art music (of which orchestral film music is a branch), going back to evocations of Turkish/Janissary music in Haydn, Mozart and Beethoven (and less well known examples from earlier in the 18th century, as well). Debussy was, like most everyone else in high-culture France around the turn of the 20th century, fascinated by the Far East and incorporated many of its topics into his own music (e.g., pentatonic scales and gamelan-like gestures).
Musical semiology is an extremely fertile research area these days, there are dozens if not hundreds of scholars working on various aspects of signification, topics, musical meaning, and aesthetics. Too many to list specific citations here, really (one exception below), but a few of the heavy hitters in the field are Jean-Jacques Nattiez (older and primarily ethnomusicological, but established a lot of the basic terminology and concepts still in use today), Eero Tarasti (often considered the founder of Western musical semiology), Anthony Newcomb, Kofi Agawu, Robert Hatten, and Raymond Monelle.
On semiology in popular mass media in particular, I would recommend Philip Tagg's Ten Little Tunes (2003) and Music's Meanings (2013), the latter of which is specifically intended for non-musicologists.
/u/CptBuck on Belly Dancing, "The Streets of Cairo" and late 19th century world fairs will probably interest you: https://www.reddit.com/r/AskHistorians/comments/4o2243/tuesday_trivia_forgotten_cultural_fads_and/d492g0f?utm_source=reddit-android/