The deadliest war in american history

The American Civil War was a war between the states of

america - its America - always CAPITALIZE countries, languages, proper names

 from 1861 until 1865.  - You need a full sentence here: The war lasted from....

The U.S. federal government (The "Union") was led by Abraham Lincoln, who lived from 1809 until 1865, when he was shot during the Civil War. He was an opponent of slavery in the United States

and before becoming the first republican president of the United States, he was a lawyer. - again here: start a new sentence (There needs to be a commar separating sub clause and main clause!!)

The "enemies" were the eleven southern slave states, which formed the Confederate States of America and were led by Jefferson Davis. The war began April 1861, when forces from the South attacked a U.S. military installation. Then, both sides built armies to fight

against the others. - better: each other

 September 1862 Abraham Lincoln held a

speach, - tapo: speech

 which was called the Emancipation Proclamation and made clear that ending slavery in the south was his goal of this war. The Civil War of America is also called the deadliest war in american - again: America

history because over 620,000 soldies died. It ended April 1865

as - it needs to be when here

 the resistance of the southern states finally broke.