Why some people think my God is greatest?

there can be only one.

In fact there is only one God Almighty,having different names as ALLAH,BHAGWAN,ESHWAR etc.......Yes,He is the GREATEST,the most Powerful,the most Merciful and the most Forgiving......We do not have separate Gods........Please try to recognize this one God,without associating any self-created mediators like priests,monks,prophets,idols etc.........He never likes Polytheism and it is the biggest and the only unforgivable sin in the last divine book,the Holy Quran........

i think it comes from a need to believe that their particular belief is both literal and the only one - not just a version of something or one way of seeing.

There is truely only one God. There are just several different names for Him. A lot of the differences are the interpretations of the Bible and whether or not the person believes in the Bible in the first place. Are you saying that there are a lot of fanatics in the world? Did I understand you correctly? If so, I hope and pray that you are right, because one day we will all have to answer for our wrongs. But sadly, I feel that the world is going in the wrong direction and that many will be lost! Hope this answers your question.

It is our belief. Beliefs are unexplainable feeling like faith. Faith which is not seen but only believed. Fanaticism does exist cause it's a strong automatic emotion that defends our beliefs, i guess.