It seems like World War Two was fought very differently to World War One both in terms of speed and style of combat. What led to this change in style of conflict? Was it better technology or something else?
Not a flaired historian, but I can answer this one with 3 things; tanks, long range artillery and airplanes.
With the introduction of tanks the idea of entrenching yourself became very dangerous. Following behind a tank made it easy to cross a battlefield that didn't have anti-tank weaponry. Next, you have long range artillery. Sitting miles away you could shell an area. Whereas previously you needed line of sight to properly place shells. Lastly, airplanes allowed people to fly over the battlefield and land behind the lines. Therefore, watching one direction was very dangerous.
I would like to finish off with one last thing. I'm not saying this is 100% or the reason for the end of trench warfare. I'm saying that these three things heavily influenced the changing of strategies used during combat. You now needed to break line of sight and use camouflage to avoid aircraft detection. Meaning you couldn't sit out in a field and duke it out. You needed buildings, trees, and earth to protect you from prying eyes.