One post drive 100 and other 50 drive around 100 only...why?

It's because the single post driving 100 visitors will be ranking well in the Google or other search engines which you may easily check by searching that topic. The other reasons may be use of appropriate keywords, relevant content, but the most is its ranking in Google b'coz that's the main fact that drives traffic. Your other posts which are collectively driving a traffic of 100 visitors might not be up to the mark.

This is because of missing of keywords, irrelevant articles and will be ranking very low in Google and search engines.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.