Technological advances: the rifled musket.

 Some things move slowly.  The British Army issued a smooth bore flintlock musket, Brown Bess it was called, for nearly 100 years.  Infantry tactics were worked out.  You have your men load their muskets and fix bayonets.  You close with the enemy, very close.  Don't fire until you can see the whites of their eyes was the order given at Bunker Hill.  That's probably 20 feet, so close you cannot miss even with a smooth bore.  After firing on the enemy  you went at them with bayonet and gun butt.  Nobody got a chance to reload.  This state of affairs lasted up thru the Napoleonic wars.

   Come forward to the American Civil War.  All the new Army officers, recently pulled from civilian life, are furiously reading Jomini, Napoleon's biographer/historian.  Both Civil War armies, Union and Confederate figured Napoleon knew land warfare, he won a number of striking victories.  The Americans figured if it worked for Napoleon it ought to work for them.

There had been one important technological change since Napoleon's time.  The muskets were now rifled. The troops could open fire at 200 yards (600 feet) and get hits.  Rifling had been around for a couple of hundred years, problem was, using a round ball in a muzzle loader, it was quite difficult to force the ball down the barrel.  The ball had to be big enough to take the rifling, which meant the rifling had to cut grooves in the lead ball.  So, rifled guns were made, were used, but they were so slow to load that armies issued faster loading smooth bores.  

   The French solved the problem with the invention of the Minie ball, a lead slug with a hollow at the back.  The explosion of the gunpowder forced the hollow rear end of the bullet to expand and take the rifling.  The Minie balls were cast small enough to just drop down the muzzle, just like a smooth bore.  So now we have a rifled musket, that loads as fast as the old Brown Bess smooth bore.  And it is in mass production, issued to most of the troops at the start of the Civil War and issued to all troops by the end of the Civil War. 

    So now we consider the effect on infantry tactics.  The defender, standing his ground, can open fire when the attackers are 200 yards away.  By the time the attacker has charged 200 yards, the defenders have time to reload, at least once, and give 'em another volley.  The defenders get at least two shots for each man.  The attackers only get one.  Muzzle loaders cannot be reloaded on the run, you have to stop, stand still, to get the powder, the Minie ball, and the wad down the barrel, to say nothing of getting the percussion cap on right.

   That's what happened to Pickett's Charge.  Union infantry shot Pickett's men down before they got close enough to use the bayonet.  And something similar happened at all the Civil War battles.  Defenders always defeated attackers.  This was not supposed to happen if you had read your Jomini.