Belgium is split down political and language lines.
Belgium is split down political and language lines.

i 've checked "split" in a dictionary.but i failed to find "split down". is the sentence above right？if so,please explain it precisely,thank you!

Question

Belgium is split down political and language lines. 
Belgium is split down political and language lines. 

i 've checked "split" in a dictionary.but i failed to find "split down". is the sentence above right？if so,please explain it precisely,thank you!

Answer

It means the society is split (=not united). There are two languages in Belgium, and society is split according to those who speak French and those who speak Flemish. There's also a German speaking population but that is very small.
down those (linguistic) lines = according to the languages spoken by different groups