For us Japanese, this may seem strange. Japan has always been a single country, and we are not familiar with countries changing or disappearing. This is because Japan is a very peaceful country.
However, there are still wars going on all over the world. There are still many places where one country is divided into many countries.
A war within a country is like a war between Tokyo and Osaka in Japan. What would happen if such a war were to take place in Japan? Japan would probably split into two countries, Tokyo and Osaka. In this case, the number of countries would change from one to two.
There are many such countries in the world today. There, even children as young as elementary school students are taking part in wars with guns. Japanese children can go to school, study, play, and eat delicious food every day because Japan is at peace. We should be thankful for this peace.
This is a bit of a digression, but it is impossible to give an exact number of countries in the world. If it is an approximate number, there are about 200 at present. However, this number may change in a while.