Voted for the civil war.
Many of our racial and political divisions can be traced directly back to slavery. Slavery isn't the direct reason why African Americans vote 90% for the Democrats, but the issues resulting from slavery and the civil war have caused AAs and southern whites to be as politically polarized as they are today.
The confederate flag issue, the BLM movement and the backlash to it are all modern day echoes of that time in our history when we were never more divided.
#2 would be the Founder's era. #3 would be the Great Depression-WWII. Its no coincidence that these three eras are associated with some of our most well known and respected presidents.
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