Consequently, the parties switched sides shortly after the civil rights act of 1964 passed. What you are seeing today is the result of decades-long efforts coming to fruition for that conservative-racist party.
Explanation: In 1865, Radical Republicans were called such because of their radically pro-civil rights platform, including the abolition of slavery and total legal equality for Black Americans. They were later be instrumental in passing Federal anti-segregation laws (which, unfortunately, were struck down by the Supreme Court).
… I could not guarantee the same for 2021 ‘radical’ Republicans.
the slavery/anti-slavery thing was always a north-south thing, not a democrat-republican thing. Republicans were powerful in the north and then their base shifted to people from the south. Democrats shifted northward. As they shifted, so did their stance on things.
The Republican Party was formed, explicitly, as an anti-slavery party.