The Reconstruction Era in the United States occurred because of the conditions of the South after the Civil War.
Lincoln probably would've never been assassinated if it weren't for the Civil War.
In my country (Canada), the Civil War was actually one of the primary motivations for Canada to head towards Confederation (when we became a Dominion of Britain and had our own government and could decide our own domestic policies) because we were afraid of an invasion from the United States. So the Civil War helped create Canada.
The settling of about 8000 or so slaves in Western Africa created Freetown in Sierra Leone, which is now their capital, so very important African history there.
The Civil War advanced war technologies to previously unseen heights. World War 1 was where the machine gun came to prominence, but the Civil War was where they were first used. More than one shot rifles and other weapons started to be used.
The Civil War was very important in numerous countries history.
