Step changes in aircraft were always engine driven
1) A piston engine with a high enough power to weight ratio to allow flight: The Wright bothers engine
2) A piston engine with enough power to give meaningful performance: The Gnome rotory
3) A piston engine that can produce enough horsepower to make air transport practical. The P&W and Curtis 9 and 18 cylinder radial engines
4) The first jet engines
5)???