Why was line warfare used?

The line formation is a standard tactical formation which was used in early modern warfare. The line formation provided the best frontage for volley fire, while sacrificing maneuverability and defence against cavalry.

When did Infantry stop fighting in lines?

Infantry ceased wearing it almost completely after 1660, and the armour carried by cavalrymen grew steadily shorter until all that remained were the breastplates worn by heavy cavalry—the cuirassiers—as late as the 20th century.

Was fighting in lines an outdated strategy in the Civil War?

Yes, fighting in lines was an outdated strategy with the technology used during the Civil War. The most concise way of explaining why, that I can think of, is the fact that old ideas die hard when it comes to military strategy and it has been that way throughout history.

Why did the American Civil War involve fighting in close knit formations?

Fighting in close formations was slowly becoming obsolete but you have to remember that neither side in the ACW was professionally trained other than the small part of the U.S regular army. Fighting in close knit formations made the communication and execution of orders much easier which the untrained officers on both sides needed.

Did armies used to stand in lines and kill each other?

I just discovered The Armchair Historian, a rather endearing YouTuber who created an animated history lesson about why armies used to stand in lines and kill each other. It seems counterintuitive now that we have weapons designed to kill large quantities of people and traditional wars between nations have given way to asymmetrical conflicts .

How were battles decided in the American Civil War?

Battles in the ACW were typically decided by which side broke first, not which suffered more casualties in the charge. The side that broke would then suffer terribly at the hands of pursuing infantry or cavalry if it was on the scene.