There have been many times in history where people have been treated unequally. Let me list a few of them.
First, the holocaust was a time when Germany treated those whom they deemed foreigners with inequality in the worst possible way. In particular, under the leadership of Hitler over a million Jews were put to death. It is estimated that over million died in the Auschwitz prison camp alone. This was unequal treatment and then some based on race. What is most shocking about this is that it took place in our modern world. In fact, it took place within the living memory of many people today.
Second, if we move closer to home, there has been unequal treatment based on gender. If you think about it, there was a time when women were not allowed to vote. It was only through the hard work of activists that the government gave the right to vote to all women in 1920 (Nineteenth Amendment). Even now at times there is unequal and unfair treatment towards women in many other subtle ways.