system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did people stand side by side during battles in old wars?
gpt
You are talking Napoleonic "everybody in a line and shoot"?

It has to do with the accuracy of early firearms.  Until the invention of rifling, guns were not all that accurate.  The solution was to get a bunch of them together and fire them all at once.  While any individual shot was inaccurate if you put enough bullets into the air some will surely hit the target.

That's how those formations developed.  It was an efficient method of delivering maximum firepower with the weapons of the era.