So, ... the greatest threat to the world is ...?

It depends.

The answer depends on whom you ask.  In the Arab world (ht)?

73 percent of respondents believe that Israel and the US are the two countries presenting the largest threat to the security of the Arab world, with 51 percent believing that Israel is the most threatening, 22 percent believe the US is the most threatening, and 5 percent reporting a belief that Iran is the single country most threatening to the security of their countries. 

Reminds me of the time that when I was introduced as one coming from America, an Arab immediately said that I was coming from a terrorist country and I was guilty by association!