Complex sentence: States arising out of the Austro-Hungarian and Ottoman Empires had huge numbers of ethnic populations outside of new boundaries and several had long standing diasporas inamicable to 20th century European nationalism and state creation.
Split into simpler sentences: States arising out of the Austro-Hungarian and Ottoman Empires had huge numbers of ethnic populations outside of their new boundaries. Several had long-standing diasporas that did not conform to 20th century European nationalism and state creation.