When ever was America greater than today?
When they were fighting in WWII and helping to keep the world free. When they were coming up with the ideals and principles that are "the shining city on the hill" even if they don't always live up to them.
When they abolished slavery and granted freedoms - that had never happened in the history of the world up to that point.
There are plenty of times the US has been great or done great things. If you only want to see the negatives and are willing to cherry pick from a minority of people from hundreds of years ago to paint everyone as bad then of course you won't see anything good. It just means you're a hateful bigot.