In 1619, Europeans started the slave trade, which involved kidnapping Africans and shipping them over to America to be sold into slavery. These Africans were treated horribly.
Eventually, slavery became a big part of American society and the children of these Africans were sold into slavery too.
Throughout this period, brave people did what they could to overcome adversity, end slavery and secure equal rights for African Americans. This was a long process, but thankfully there have always been people with the drive and passion to make things right.