Actually, try just about every European, Asian, African and South American country. OK... Maybe not every country, but a good 75-85% went through periods of slavery, genocide, you name it.
No they didn't. Only the USA had slavery. I don't know what history books you have been reading.
It's sad that our librul wimps allow the world to put us, the youngest nation, in the spotlight for having enslaved a race of people when things like this (article) have happened even more recently and no one knows of it. Ask the world what the biggest atrocity ever committed by a country is and they'll all say US slavery. And then a large group of people here will stand up like idiots and agree.
<warning first line full of sarcasm>