Gunpowder
Iron Bridge
Do you mean, what invention utilised during the Civil War changed combat? The rifle-barrelled cannon. Or the minie-ball. The post-war invention would have been the machine-gun.
Aerial vehicles
gunpowder and the abacus.
Before the explosive devices were invented, fighting completely required strength (for example using swords, arrows etc.) and never relied much on heat to kill the enemy. The invention of the explosive devices changed this.
World War 2 changed the world forever by teaching us a lesson in the areas of atomic warfare, and the treatment of war prisoners.
Gunpowder - Tseng Kung-Liang made the formula publicly available in AD 1040.
Gunpowder: once used in warfare, it made it's way along the silk road to India, the Middle East and Europe.
The machine gun changed warfare
The invention of the Firearm
zeus-- > Athena is a Goddess .
How about this? "The Civil War was the birthplace of technologies that changed the nature of warfare forever."