If one measures, whether war could be prevented -
the demonstrations were then no success,
because - as it appears - the ones which want war - continue their way unimpressed.

But the demonstrations were a great success in sense
--- the people (through all nations and cultures, from Nord and South, from East and West) illustrated that they want to exist with each other in friendship and that problems should be handled in leadership of the UNO and that the world not want to be leaded of a small group of people from the USA.
It is especially stressed
A small group because the majority of the US citizens is also against this war.

The demonstrations were a giant success because this difference was shown clearly by the demonstrations:
This group that want war do not represent the majority but only a SMALL minority.