It's not that the international community didn't know about it, simply that Turkey is far too important to sour relations with over something that happened so long ago.
As a successful and democratic (the odd military intervention aside
) Muslim country, Turkey is of huge importance to Western leaders seeking to show that they aren't crusading against Islam. For the EU in particular, the importance of a Muslim country that is practically begging to join cannot be overstated.
Besides, lots of countries don't teach about their darker periods. The Japanese have a rather woeful record in this record but it hasn't stopped them from being treated as a close partner by other nations. At least in my experience, the Brits hardly mention Empire in their schools.
For what its worth, I think Canada and France have every right to pea in their cereal. Within the EU however, especially with regards to Turkey joining, this issue often serves as a cover for the real reason for opposition - racial.
One question worth asking - what good would acknowledging this as genocide do? Are they supposed to compensate the grandchildren of those affected? Is it right that current Turks should pay for the crimes of Turks nearly 100 years ago? After all, it's changed a lot since then.