Sauron was said to have kept the 9 rings given to the Nazgul. I read an article which claimed if the Nazgul had their rings they would have been even greater in power. If this is true, why would Sauron take their rings from them? Which got me thinking: maybe without the one ring Sauron could only control the Nazgul if he held the 9 rings that were given to the Nazgul.
Is there any evidence which might suggest Sauron had to take the 9 rings of the Nazgul to keep them bent to his will?