Why was it a long time before people began to object slavery? what finally led people to try to abolish slavery?

Like i said on the same Q from someone else, its probably because it was the cultural norm for a while. But eventually, some people thought of it as incorrect and campaigned against it.

from the conditions of the working class in england by friedrich engels,the main idea is :

payments were made after the 1940s.

in the 1980s, a commission held investigations and made recommendations.