Kurt Volker was the US ambassador to Nato from July 2008 until May last year.
He says Nato members from central and eastern Europe want protection from Russia whereas those in the West want "strategic engagement" with Russia.
This week Nato released its mission statement for the next decade which includes winning the war in Afghanistan and countering Iran's missile programme.
Can the 28 member military alliance meet such a diverse range of challenges?
You can watch HARDtalk on Wednesday 19th May on BBC News Channel at 0430 and 2330 BST and on BBC World News at 0330, 0830, 1530 and 1930 GMT.
~RS~q~RS~~RS~z~RS~52~RS~)
Bookmark with:
What are these?
E-mail this to a friend