How is the US marking 400th anniversary of slavery?

Sort it of a misleading title. The United States did not exist until 1776. If I do the math correctly the US has only been around 242 years. Slaves were emancipated in 1865. So we can only mark the 99 years the US had slaves or we can mark the 242nd anniversary of the beginning of slavery in the US. . Are the British and Spanish marking the 525th Anniversary Of slavery by European nations in the Western Hemisphere? Of course Aztecs and other indigenous people had slavery long before Europeans arrived. The indigenous people in the land mass called The United States also practiced slavery . So when did slavery really start in the Western Hemisphere? Maybe instead we should be celebrating the US Quakers who came up with the strange notion slavery was anti-Christian. This odd notion bleed over to England and underpinned the work of Wilberforce and others who managed to make slavery unlawful in England that lead to the eventual banning of slavery in The United States of America. Were those indigenous people who suffered under slavery any less miserable than Africans brought to the Western Hemisphere and suffered under slavery?

We still have human trafficking; how about we abolish it in the USA? Just change the name it will go away?

I dunno...maybe ask the 3,500+ Union soldiers buried at Gettysburg National Cemetery.