Basically just the board game Risk.
Print out the map, divide it into 9 pieces of paper so it's a decent size.
Distribute to tokens to teams of 3 or 4 students, and let them choose 3 regions each to place tokens.
There are 21 regions of the world (not the best names, but I was trying not to play favourites and get the kids using North/South/East/West and the names of the continents).
NOTE: There will be three regions left over, group janken against the ALT to get them
They choose what team they want, janken for any disagreements, janken for who goes first, and then say:
“I want to attack _________” and they janken for who wins the fight. The attacker gets the region if they win, and the defender doesn’t lose their nation if they win.
The team with the most nations at the end is the NUMBER ONE INVADER
Notes:
Try to encourage janken in English “Rock, paper, scissors, 1, 2, 3”