l'd read it slightly differently.  The Romans didn't need to impose their gods cos they had sufficient control without bothering.  Their policy was to rule lightly from afar.  It is only relatively recently (Crusdades onwards) that invaders have used religion as a weapon and a means of oppression.  Now as over-population threatens such things as access to oil, fresh water, etc, everything has gone up a gear. 

The one saving grace currently is that there is more than one religion out there.  If there was just one, the chances of being forced under its umbrella would be high ... and the consequences grave for humanity.