There is a much quicker and simpler way of completing Mission 1 than the method of obtaining the Lightning Spells and training up Warriors which you are supposed to use.
Instead, just build Huts until you have 4-6 of them on the starting island (use the Land Bridge Spell to create more land to build them if need be), and have your Shaman pray at the stone head on this island to obtain two Land Bridge Spells for the crossing to the enemy territory. Cast the Land Bridge Spell to the central island, pray at the Vault of Knowledge to obtain the Warrior Training Building for future Missions, and cast another Land Bridge Spell to the enemy Shaman's island. Gather all of your Braves, and have them target the hut on the island, then the Shaman. By this time, you should have enough Braves to win by simply outnumbering the enemy.
On the first island, highlight and press X on every tree. Then press start and there should be a cheat menu if it was done correctly.