Holocaust is associated with another war, the Second World War. Ethnic diversity is a concept that goes against the actions of Serbian nationalists: they wanted less diversity, not more.
Also, Depopulation is also connected with what the nationalists did, but since they didn't attack all people, but only people of certain (other) ethnicity, Ethnic Cleansing is the best answer.
The blockade was supposed to prevent the South from getting resources and support from other countries who would support it such as those in Europe who were ready to recognize it as independent and help it if it meant that in the long run it would help them by weakening the Union.
