The first every tank used in combat was the british in world war one 1916. This is one of the very first tanks ever used in warfare and was a slow and unreliable.
During World War Two the Germans started to rearm and started to create them in 1934 starting as the panzer 1 and panzer 2
The creation of light, medium, and Heavy/super Heavy tanks changed the battle by bigger and faster than before. Medium was the best to have like the T-34-85 more medium tanks came into service in 1943-1945. The T-34-85 is still being used to this day.
The M1A2 is one of the best but costly at around 8.58 million per unit. But the why the tanks armor is and the speed shows us that the engine could change the speed and how much the armor could be.