How was command and control improved during the US Civil War?

Answer 1

The US Civil War saw a vast improvement in the way communications helped coordinate the armies on both sides of the conflict.
For the most part, electric telegraph lines ran along side of railroads. And, at the terminals of the telegraph were dedicated professional signalers who accepted a measure of military supervision in return for exemptions from the drafts. The Union had more technological advances than did the South in the arena of communications. By 1865 the US Military telegraph system had developed into a wide ranging and sophisticated operation. Telegraph communications between Washington DC and its armies could be updated on an hourly basis and could provide in great detail the actions on various battlefields.
On the battlefield themselves, tactical decisions and commands from a generals' headquarters were relayed by a flag system in daytime and by lights at night.
As one example is the US Civil War Battle of Fredericksburg in 1862. There General Ambrose Burnside was in telegraph communications with President Lincoln. Reportedly Lincoln encouraged Burnside to attempt a frontal assault on fortified Confederate positions.