Question

Please give me simple explanation of what is civil war

Answer 1

war within a country between two groups

Answer 2

Heyo!
A civil war is a war in which two or more groups fight within the same country and sometimes, its misconceived as a war between two countries, but that's not the case.
So, in a civil war, it's either different groups of people fighting against each other or the army fighting against a part of the population.
For instance, in Iraq, you have the Shias and the Sunnis, two different sects of Muslims, fighting for several years.

Yes, there are problems after a civil war because people have to live in the same country with whom they were against, which is slightly ironical.
Also! In such a war, the worst outcome is that neighbours often become enemies unexpectedly.