Geographic ranking difference

I am currently 9th on google . c-o-m (usa)
And 2nd in google . c-o-m (international)

I am wondering why such a big difference?
In usa google same sites are before me that i outranked on the international google.

I didnt set anything in webmaster tools. Does it even have any effect if you set geographical target? How long until you see difference?

thanks

You need more US based backlinks.

And how do you know which are US Links except searching for site:us ?