On December 6th, 1865 the 13th Amendment was ratified.
This Amendment, as you all probably know, ended slavery.
This holiday should be named in such a way to express the freedoms of the occasion, and not remind us of the horrors it had to end. An example of a name that I believe sounds both strong for it's meaning in the past as well as holding true for our current day in history is the following:
National Freedom Day