The Sepratist Army invades the Wookiee home planet of Kashyyyk and attacks. This was the first of many Sepratist invasions throughout the Galaxy. The one on Kashyyyk is significant, as Ki Adi Mundi makes a brief reference to this at the Jedi Council.
"What about the Droid attack on the Wookiees?" - Ki Adi Mundi
Yoda was sent to Kashyyyk to aid the Wookiees after he mentioned it. Mundi was then dissapointed as he wanted to go and help the Wookiees. However, he was already on a mission on Mygeeto. This indeed is a true tragedy for sure. How ironic that he was the only one who thought of it and yet Yoda went instead.