Complex sentence: Mestizo population in Argentina, unlike in other Latin American countries, is very low, as is the Black population after being decimated by diseases and wars in the 19th century, though since the 1990s a new wave of Black immigration is arriving.
Split into simpler sentences: Mestizo population in Argentina, unlike in other Latin American countries, is very low. So is the Black population after being decimated by diseases and wars in the 19th century, though since the 1990s a new wave of Black immigration is arriving.