There have been so many genocides in the past century.. from the Holocaust to genocides in Indonesia, Bangladesh, Serbia, Bosnia, Rwanda, Cambodia, Armenia, Burma, the list goes on... is this quantity unprecedented/unique in human history? Does it have anything to do with the huge increase in populations throughout the world, or something else?
I would think that it has more to do with the rise of nationalism more than anything else.
Nationalism was a product of the late 18th and 19th centuries.
As people started to coalesce into national identities unified by language, history (real or fabricated), folklore, religion, etc. these nations also tended to associate themselves with geographic boundaries.
Smaller nations or ethnic groups that fell within the same boundaries could become prime targets to displace, kill, subdue and/or scapegoat in order for the dominant nation to expand.
Prior to that, boundaries of states and empires tended to be more fluid as the ruling noble classes could wage war for resources with little care for what ethnicities their subjects came from or without associating their Empires with any kind of fixed borders.
When the Jews fled into the Ottoman Empire to escape persecution in Europe in the Middle Ages, they were tolerated within the Empire. But when we see such diasporas in more recent times, such as when the Jews started to move to the Middle East after WW2, there’s a greater nationalist reaction against them and the belief that they don’t belong there.
And when during the Civil War when the issue of emancipation came up, the idea of deporting African American slaves back to Africa was even considered.
There forms a greater sense of what constitutes (or what should constitute) a “nation” and can lead to an “us vs them” mentality.
The increase in technology coupled with ultranationalist sentiment I feel is to blame for the increasing severity of genocides in the past century.