What is natural increase? what can it tell us about a country?

RNI excludes in-migration and out-migration, giving an indication of population growth based only on births and deaths. RNI can indicate what stage of the Demographic Transition Model (DTM) a country is in. Trends in RNI can predict a country's economic stability, level of development, and other things.
The human sex ratio, which is usually defined in terms of the number of males per 100 females, varies greatly between countries and regions. The biological norm is for the sex ratio at birth to be about 105 more or less everywhere – meaning just over 51% of births are boys and just under 49% are girls.

Ongoing civil wars western roman empire finally collapsed476 c.e. romulus, the last of theroman  emperors in  the west, was overthrown by the germanic leader odoacer, who became the first barbarian to rule in rome. the order that the  roman empire  had brought towestern  europe for 1000 years was no more.