All pulled from Wiki:
British. No war required.
In 1772, the Somersett Case (R. v. Knowles, ex parte Somersett)[311] of the English Court of King's Bench ruled that slavery was unlawful in England (although not elsewhere in the British Empire). A similar case, that of Joseph Knight, took place in Scotland five years later and ruled slavery to be contrary to the law of Scotland.
Following the work of campaigners in the United Kingdom, such as William Wilberforce and Thomas Clarkson, the Act for the Abolition of the Slave Trade was passed by Parliament on 25 March 1807, coming into effect the following year. The act imposed a fine of £100 for every slave found aboard a British ship. The intention was to outlaw entirely the Atlantic slave trade within the whole British Empire.
The significance of the abolition of the British slave trade lay in the number of people hitherto sold and carried by British slave vessels. Britain shipped 2,532,300 Africans across the Atlantic, equalling 41% of the total transport of 6,132,900 individuals. This made the British empire the biggest slave-trade contributor in the world due to the magnitude of the empire. A fact that made the abolition act all the more damaging to the global trade of slaves.[312]
The Slavery Abolition Act, passed on 23 August 1833, outlawed slavery itself in the British colonies. On 1 August 1834 all slaves in the British West Indies, were emancipated, but still indentured to their former owners in an apprenticeship system. The intention of, was to educate former slaves to a trade but instead allowed slave owners to maintain ownership illegally. The act was finally repealed in 1838.[313]
Britain abolished slavery in both Hindu and Muslim India by the Indian Slavery Act V. of 1843.[314]
Domestic slavery practised by the educated African coastal elites (as well as interior traditional rulers) in Sierra Leone was abolished in 1928. A study found practices of domestic slavery still widespread in rural areas in the 1970s.[315][316]
France, no civil war required:
There were slaves in mainland France (especially in trade ports such as Nantes or Bordeaux).,[317] but the institution was never officially authorized there. The legal case of Jean Boucaux in 1739 clarified the unclear legal position of possible slaves in France, and was followed by laws that established registers for slaves in mainland France, who were limited to a three-year stay, for visits or learning a trade. Unregistered "slaves" were regarded as free. However, slavery was of vital importance in France's Caribbean possessions, especially Saint-Domingue. In 1793, influenced by the French Declaration of the Rights of Man of August 1789 and alarmed as the massive slave revolt of August 1791 that had become the Haitian Revolution threatened to ally itself with the British, the French Revolutionary commissioners Sonthonax and Polverel declared general emancipation to reconcile them with France. In Paris, on 4 February 1794, Abbé Grégoire and the Convention ratified this action by officially abolishing slavery in all French territories outside mainland France, freeing all the slaves both for moral and security reasons.
Napoleon sent troops to the Caribbean in 1802 to try to re-establish slavery due to the economic stress France was suffering while fighting all over Europe. They succeeded in Guadeloupe, but the ex-slaves of Saint-Domingue defeated the French corps that was sent and declared independence. This colony became Haiti, the first black republic, on 1 January 1804, with at its head the leader of the revolt, Toussaint Louverture.[95] Slavery in the French colonies was finally abolished only in 1849.
It goes on. War is not needed to end slavery. Hate to break it to you......
Was it needed in the US? Yes, if the goal was to keep the US together as Lincoln needed. Once again because South Carolina was extremely paranoid.