You may want to be more specific - countless technological advancements have contributed to the kind of combat aircraft we see today. If we ignore electronics (which nowadays are arguably the most important part of combat aircraft design) and armament, the biggest areas of improvement are engines and propulsion, aerodynamic design, and materials. I'll try to do a broad overview of things - let me know if there's anything specific you want me to elaborate on.
The triplanes made famous in WW1 - the Sopwith Triplane and Fokker Dr.I - were alarmingly simple aircraft. They were largely made of canvas stretched over a wood frame with wires spanning around the aircraft to provide structural support to critical areas like the wings. Structural support would be the driving reason behind the biplane and triplane layouts, as the wings could be braced off of eachother with wires and struts. Airfoils - the cross-section of the wing - were very rudimentary, often consisting of just a single layer of canvas stretched over the top of an airfoil-shaped wood frame. Engines were perhaps the most terrifying feature of these designs - the rotary engines popular during WW1 were mounted in such a way that they spun with the propeller. Combined with the very light construction of the airframe, the several hundred pounds of engine spinning at the same speed as the propeller on the front of the plane led to dangerous gyroscopic effects that made the aircraft very difficult to control at low speeds. On the topic of the propulsion, propellers of the time were simple fixed-pitch propellers and almost always two-bladed.
Going forward, every aspect of these aircraft would be improved upon. Better structural design and materials would allow for simpler biplane structures with fewer wires and struts or even monoplane designs if the wings were made thick enough. New materials contributed to this, particularly the aluminum alloy known as Duralumin, which would make the use of metal in aircraft structures feasible. The first all-metal aircraft - the Junkers J I - appeared during WW1 and in fact was a monoplane, but metal construction would catch on more commonly by replacing the wood structure underneath the canvas with metal tubing. All-metal designs would become the norm during WW2, although control surfaces often remained canvas-covered frames even in otherwise all-metal designs. Aerodynamic design massively improved, with groups like NACA (predecessor to America's NASA) doing huge amounts of research in the design of airfoils, engine cowlings, and various other aerodynamic features. New developments in propulsion would allow engineers to make the most of these new aerodynamic developments. Through the interwar period, engines became significantly more powerful and, perhaps more critically, significantly more reliable. During WW1 and the early interwar period, it was common for large multi-engined aircraft to have the engines serviceable in flight (see many of the Riesenflugzeug Germany used in WW1). Come WW2, however, such a feature is unheard of on aircraft - engines were reliable enough for even long endurance flights. Whereas the Fokker Dr.I mounted a 110 hp rotary engine in 1917 and the one of the premier aircraft engines at the end of the war was the American 400hp Liberty engine, fighter engines by 1939 were of the 1,000 hp class - the DB 601, Rolls-Royce Merlin, and Hispano-Suiza 12Y. By the end of the war, engines like the Wasp Major were pushing to nearly 4,000 hp. Just as important as added engine power was improved propeller design. Variable-pitch propellers would become commonplace in the interwar period, allowing the pitch of the propeller to be tailored to factors like the speed of the aircraft, air density, and RPM of the propeller. The ultimate result of these developments in propulsion was that aircraft were able to become faster and - more significantly - heavier.
Once we get to the postwar era, some new factors become important. The increasing speed of aircraft during WW2 had seen aircraft pushing up against supersonic flight at the extremes of their performance, but it wouldn't be until after WW2 that engineers were really capable of designing for transonic flight. The theory of supersonic flight had largely been figured out during the interwar period, but the kind of understanding of transonic flight necessary for supersonic aircraft wasn't developed until after WW2. Developments like swept wings, conically-cambered delta wings, and area-ruling would further contribute to high-speed flight, and would have applications outside of supersonic aircraft (as we see with modern airliners). New propulsion also drastically changed flight profiles. Both piston engines and turbines lose power as altitude increases, but turbines proved more suited to high altitudes thanks to their greater power/thrust output. Jet engines replaced propellers for most applications, and where propellers remained, they were most often replaced by turoprops - effectively a propeller powered by a jet turbine - to provide a more powerful powerplant in a more compact and lighter package.
From there, however, surprisingly little has changed in the grand scheme of things. Most of the advances for several decades have been the introduction finite-element-analysis using supercomputers for aerodynamic analysis (alongside wind tunnels), new materials improving structures and powerplants, and electronics (both hardware and software) improving capabilities of airframes.