What are the effects of the civil war?

 The South was placed under military rule and divided into military districts. Southern states then had to apply for readmission to the Union. 
The nation was reunited and the southern states were not allowed to secede.
 The Federal government proved itself supreme over the states. Essentially this was a war over states rights and federalism and the victor was the power of the national government
Slavery was effectively
 ended. While slavery was not officially outlawed until the passage of the 13th amendment, the slaves were set free upon the end of the war.
Reconstruction, the plan to rebuild America after the war, began.

The Civil War was one of the most tragic wars in American history. More Americans died then in all other wars combined.