The West, and specifically America, is blamed not so much for slavery but for the following things all together:

1. Chattel Slavery

2. Racism as a form of pseudo-scientific theory that established why different "races" were of lower quality than others, and thus any member of the lower race deserved to be enslaved by members of the higher race.

3. Laws in various states of the U.S that established black people could be enslaved when traveling in that state, or that free black people traveling in the region would not be allowed to do so https://medium.com/luminasticity/the-free-slave-8336f214da45

4. After finding slavery unacceptable, the U.S with its pseudo-scientific cover of Racism in much of the country still treated black people as if they were enslaved, and often killed them for no particular reason discernible to reason.

5. One can argue as to the exact point that Black people became equal in the U.S, some might argue that it isn't the case yet, but anyone fairly arguing would have to concede that there are a number of Black people still living who were at least children when it was not the case that this state of equality existed - even if they wanted to argue that it does exist now.

on edit: changed either to still

It must be a nice consolation for the various European powers that their colonies breaking away seems to have absolved them of any blame not just the institutionalization of chattel slavery, but apparently also the creation of scientific racism.