How did the gernade and flamethrower effect the civil war?

Answer 1

You'd need to specify which civil war, because the modern flamethrower was developed well after the American Civil War, so it had no impact on that war. Grenades would have had very little - they did exist, but they had a fuse which had to be lit before they were thrown... much different from modern hand grenades... and thus, their use by land forces was almost nonexistent. They were more commonly used on naval ships by crew members assaulting or defending against boarding by another ship.