Why civil war happened in America ?

The American Civil War was the outcome of difference between the democratic North and the Conservative South. Slavery was indispensable to the Southern States as their entire social and economic system vested on it. Slavery had been abolished by Parliament in England in 1833, thanks to the efforts of William Wilberforce. There were in American too, persons who carved on a campaign for the abolition of slavery. Among these were Garrison who utilized his paper the Liberator to espouse the course of the slaves and Harriet Beecher the author of uncle Tom's Cabin, mobilised opinion against slavery. 

With the coming of Abraham Lincoln into province, opposition to slavery grew. Slavery was abhorrent to Lincoln. In fact the Republican Party was established with the around object of abolishing slavery. In 1860 Lincoln fought the Presidential election as a Republican ticket and war. Tension between North and South vose to fever pitch and the consequence was although volume upon volume is written to prove slavery a very good thing, we never hear of the now who instead to take the good of it by bring a slave himself.

Abraham Lincoln made it quite that slavery was a great wrong and the South had no right to Secedo . To hold the Union infact was of per amount importance. To perceive  this unity, Lincoln had to fight.

After the surrender of fort Sumter on April 12, 1861, Lincoln ordered the troops to be called up. The war that began went on for four years and generated bitterness and caused blooded. Initially the South had the upper hand but gradually the fuered against  them the secession of South Carolina followed by others from the Union. So long as the forts remained under the control of the Federal Government things were quite but once the fort of Sumter was attached and captured war became inevitable. 

While the war was going on Lincoln's Emancipation proclamation announced in September 1862, declared the slaves free in the Southern states. But real freedom for all slaves was not achieved till the amendment of the Constitution in 1865 . The war was far from over when Lincoln delivered his classic Gettysburg speech.  Fourscore and seven years ago our fathers brought forth on this continent a new nation, conceived in liberty, and dedicated to the proposition that all men are created equal. Now we are engaged in a great civil war, testing whether that nation, or any nation, or any nation so conceived and dedicated, can long endure... It is for us, the living... to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced... that this nation under God shall have a new birth of freedom and that government of the people, by the people, for the people shall not perish from the earth.

Abraham Lincoln was re-elected in 1865 and in the same year the last resistance of the South ended with the surrender of the Southern General Lee to the Northern armies led by generals Grant and Sherman.

Slavery had been done away with the Lincoln's wish had been realized. Its abolition and emancipation of slaves was of great significance for the entire world.