What were the diffrent opinion about the expansion of slavery?

For most part of history, Slavery was widely accepted because of racial and economic issues. People of different colors were seen as inferior and viewed as cheap and replaceable labour. But in 1833 the U. K ended their part in slavery in their territories, In 1863, the U. S outlawed all slavery. But it wasn't until the 1800's when opinion on slavery started to change. And even then it was hard for changes to happen due to those holding back progress.