Level 3 introduces cards and the Earth map to new Warzone players.
The level is 1v1v1v1 on the Earth map. Unlike in level 1 or level 2, player and AI's starting positions are random. This means that it can be useful to re-start the level a few times to find a starting position that you like.
Gold stars are awarded to players who complete Level 3 in 19 or fewer turns (25 on the standalone client).