Start up a 2 player hot seat game. You can play bother players, you only need one controller.
This is doable by choosing the Y button option from the scenario menu.
You will need to play just a bit into the scenario, long enough to build close to the other player, and to be able to use spy options.
You get, capped at two instances per player;
3 casus belli for insulting a player (6 max)
5 for taking a claimed sector (10 max)
3 for being caught using spy options (6 max)
2 for attacking a unit trespassing in your territory.
A max of 3 for the "fabricate casus belli" spy option.
Simply do actions adding up to at least 15 points towards one player, and have that player declare war on the other.
Happy hunting (>*_*)>