Complex sentence: Large hotel chains typically have direct connections to the airline national distribution systems (GDS) (Sabre, Galileo, Amadeus and Worldspan) that in turn provides hotel information directly to the hundreds of thousands of travel agents that align themselves with one of these systems.
Split into simpler sentences: Large hotel chains typically have direct connections to the airline national distribution systems (GDS) (Sabre, Galileo, Amadeus, and Worldspan). These in turn provide hotel information directly to the hundreds of thousands of travel agents that align themselves with one of these systems.