Ouch, Byblos, I disagree highly. The Celts were barbarians out of the Roman point of view - so a strongly limited hostile view - coming out of the narrow-minded arrogance of the successor, believing only his point of view and laws are correct.
http://www.phatnav.com/wiki/index.php?title=Barbarianhere, origin of the word <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
And the downfall of the Roman Empire was due to more than being split up. This empire had simply outlived itself - the natural way of history for all large empires. Didn't your history teacher teach you this? Time was over for them - as time will be over for all empires. They're made to rise, develop and outlive themselves - sink and lose everything.
We'll see in a mere 500 yrs what will happen to the world order we know now - wouldn't wonder if Europe/USA would share the same fate as the celts and Romans - and sink back into unimportance.