What did Grenadiers do?

grenadier, soldier particularly selected and trained to hurl grenades. The earliest grenadiers (late 16th century) were not organized in special units, but by the mid-17th century they formed special companies within battalions.

How did ancient people fight?

The elite of the Persian Army were the famous Persian Immortals, a 10,000 strong unit of professional soldiers armed with a spear, a sword and a bow. Archers also formed a major component of the Persian Army. Persian tactics primarily had four stages involving archers, infantry and cavalry.

Why did armies shoot in lines?

In some cases, it was possible to overturn the enemy with just one volley at a short distance. The line was considered as the fundamental battle formation as it allowed for the largest deployment of firepower. Against surrounding enemy cavalry, line infantry could swiftly adopt square formations to provide protection.

Was fighting in lines an outdated strategy in the Civil War?

Yes, fighting in lines was an outdated strategy with the technology used during the Civil War.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 was fighting in close knit formations so effective in WW1?

Fighting in close knit formations made the communication and execution of orders much easier which the untrained officers on both sides needed. Also none of the infantry had been trained in fighting as an individual, without that the natural response to being charged by a block of infantry would be to run as fast as possible.

What would happen if there was no communication on the battlefield?

Without communication a battlefield can be a very lonely and terrifying place so whilst lines had their disadvantages they were still the best way to achieve success in the ACW. Percussion caps were also widely available at that time, at least in the Union Army. Reloads would be faster and misfires less common.

Why was the line formation still used in WW1?

You basically just answered your own question. One of the major reasons the line formation was still used was because the equipment was still very lackluster at that time. At least for a main infantry man.