While I do agree that, under rare circumstances, defensive war is a regrettable necessity, I disagree with your use of the Civil War as such an example. Almost every nation outside of the US had abolished slavery without resorting to civil war or massive bloodshed. In such light I regard the Civil war as completely unnecessary.

Examples:

In Britain the Slavery Abolition Act was passed by the Parliament on August 24, 1833 and became law August 1, 1834, whereupon an estimated 800,000 blacks held in bondage in the British colonies became emancipated. Slavery was abolished throughout the British possessions abroad. This date is remembered as Emancipation Day and celebrated as a public holiday in most of the ex-British colonies. The sum of $100 million was appropriated by the British Parliament to compensate dispossessed slave owners.

France on 27 April 1848, under the Second Republic (1848–52), abolished slavery. The state bought the slaves from the colonists and then freed them.

Argentina: 1813

Chile: 1823

Mexico: 1829

Denmark: 1848, including all colonies

Russia: In 1861 Emancipation of Serfs, releasing 20 million

The Netherlands: 1863, including all colonies

etc.

The Civil War was a terrible tragedy that did not have to happen. Slavery could have ended through peaceful means (education, activism, legislation, buying and freeing of slaves). Nations all over the world had proved this. Abolitionists in the US were making headway. This did not need to happen. I agree that slavery should not have been tolerated for one second let alone hundreds of years and all haste should have been made to put an end to it but not through war.

Did the Civil War eventually achieve an end to slavery in the US? Yes, but at what cost?

In 1860, slaves cost around 900-1000 dollars to buy (around $12,000 in 2009 dollars). Approximate number of slaves at that time, about 4 million. Cost to buy them back and free them, 4 billion. Let's compare that to the cost of the Civil War.

Human cost: ~600,000 Union and Confederate soldiers

Cost in dollars and cents, 1879 US estimate:

Union: $6,190,000,000

Confederacy $2,099,808,707.

By 1906 another $3.3 billion on Northerners' pensions and benefits. The amount spent on Southern benefits eventually well exceeded the war's original cost.

Altogether, around 14-15 billion dollars, over a 1 million casualties and the South burned, pillaged and left in ruins, the effects of which are still felt today.

4 bil to free slaves

VS.

15 bil for a stupid war, 600k dead, South destroyed

Was it worth it? Was it necessary? No.

Think about that before anyone tries to rattle the saber for more wars. The costs of war should be fully and carefully understood. Every last option should be fully entertained, exhausted, re-exhausted and damage should be incurred before war is even considered, before it's the last bitter option left. War is hell, It's not romantic, it's not patriotic, it's not noble it is not a solution to any of the worlds problems, its a horribly dismal position of last resort. It should be vehemently avoided if at all possible. Present wars included, especially. Everyone loses in war.

Any civil war buffs? Are my numbers off?

Sources:

http://www.civilwarhome.com/warcosts.htm

http://en.wikipedia.org/wiki/Abolitionism

http://en.wikipedia.org/wiki/Slavery_in_the_United_States

http://www.accessmylibrary.com/coms2/summary_0286-31087613_ITM

http://answers.yahoo.com/question/index?qid=20090103011706AAjPIlF