Cont'd
Why would a non-US national be offended that US cities are destroying monuments which glorify white supremacy and racism?
If history were being erased as you claim, then all references to the South and the Confederacy would be removed from textbooks, and no museums would exist that reference that period. There are many museums throughout the US that include exhibits about the Confederacy.  None of those places are being shuttered.  No history books are being rewritten to remove mention of the Confederacy, nor are scholarly texts being purged from libraries.  No one is being punished for mentioning the Confederacy.  
Sadly, white supremacy is alive and well in this country.  As evidenced by the many of the participants in the Charlottesville rally, the movement appears to have adherents among the younger generation.
Again, I fail to understand why the removal of these monuments would offend you.