Airline and travel stocks fell after regional airspace closures in the Middle East forced airlines to cancel thousands of flights, disrupting flights across the world. United Airlines, which has the most international exposure of all the major U.S. airlines, saw its shares drop 6% in premarket trading, while Delta Air Lines and American Airlines each dropped about 6%. Other carriers like Southwest Airlines also saw smaller drops. The closures have led to uncertainty in the travel sector, with international air travel demand increasing by 5.9% from the previous year.