Now, for some inconvenient facts. Wilberforce was not the first to call for abolition of slavery. Deists like Jefferson and the Quakers, who are not orthodox Christians by any means, were there first. Nor was England the first country to abolish slavery. Revolutionary France, considered godless by the orthodox Christians, had abolished slavery in 1794, but Napoleon, an orthodox Christian and opponent of deism, restored it when he took power.
The city state of Venice outlawed slavery in 960, Iceland abolished it in 1117, Spain did so in 1542, Poland in 1588, etc. Wilberforce gets attention for two reasons. First, English-speaking people tend to only pay attention to the history of English-speaking countries. Second, Wilberforce is promoted by fundamentalists because he was an evangelical Christian. Evangelicals are working hard to take credit for abolitionism.