In a 3 person game of Risk, whoever gets Australia wins 99.9% of the time if they play with the right strategy. Park and build up armies while the other players kill each other.
Unless 2 people decide to contest ownership of Australia, in which case the 3rd person wins 99.9% of the time.
This is less pronounced in games of other sizes, but it's still problematic.
It ruined the game in our family until we started our own house rule: Connect Eastern Australia to Argentina.