My first ever Ludum Dare entry is complete! :D

You are against a foe wielding a rather unconventional weapon; the forces of nature are destroying what was once a verdant world. As a minor spirit, use your magic powers to save the people facing extinction.

I hope the Intro window has good enough instructions as I feel I have to sleep now. In short use mouse to use powers and press end turn (or let it auto advance).

-MORNING EDIT-

Oh I never mentioned, this game was made in JAVA so you will require Java to be installed to run it. I've checked how it runs on OS/X looks like you need to ctrl-click the jar file to run it, then accept the warning about unknown developer :S The buttons are in a different style and dont fit as well but the game does work.

Well that was a tiring night, was definitely hard to focus those last few hours. Now that I've had a bit of a rest I can add some proper info on how to play.

OBJECTIVE:
To get world population as high as possible in the 500 turns. Player actions (apart from selecting tribes) take mana which is gained 1/turn.
The climate will shift, try to settle temperate regions. Arctic=death, desert=also death

GAME RULES:
Tribes (the orange squares) will wander, getting food from bushes and trees if present. When they are somewhere with no plants they will starve and decrease population. If they reach 0 population they die. Giving a tribe a goto command will make them try to travel to the selected tile.

Settlements are created by selecting a tribe (they will have a green box around them) and clicking settle, this requires mana. Settlements cannot move but can grow crops nearby to feed themselves.

Tribes or settlements that reach a high population will create new tribes.

If a tribe tries to move into a tile with another tribe or settlement in it they will attack it. Both tribes lose population proportional to the size of the other tribe.

TERRAIN:
Every map tile has a height, temperature and amount of plants.

Heights:
Ocean: tribes cannot cross and settlements cannot cultivate, can be raised up into land.
Lowland (no symbol): lowest land height, good for growing crops in mild temperatures, height can be changed.
Hills : medium height, not as good for crops, height can be lowered.
Mountains: Highest height, no crops or plants will grow here, height can be lowered.

temperatures:
Desert: Hottest region on equator, plants will only grow on coast where rain falls.
Savannah: Hot regions north and south of equator, plants and forests will grow over this area.
Temperate: Mild regions approximately equidistant the equator and poles, most fertile lands with many plants and forest.
Tundra: Cold regions near the poles, plants will only grow on coast where rain falls.
Arctic: Coldest regions at the poles, nothing grows here and any tribes which stay here too long will starve.

Plants:
These will regrow once harvested by a tribe as long as temperature is not too severe.
None (no icon): either land is barren or plants have been harvested and must regrow.
shrubs (little green specks): can feed a tribe for a turn, will regrow over time.
trees (tiny tree symbol): can feed a tribe twice (symbol goes from tree to shrub to none), will regrow over time.

POWERS:
no power selected: select tribe, used to give further commands.

sink land: drops the height of the tile clicked on until it is sea, takes 1 mana per change in tile height.
raise land: changes the height of the tile clicked on until it is low ground, 1 mana per change in height.
raise hill: same as raise land but changes height to hills.
raise mountain: same as raise land but changes height to mountains.

goto: REQUIRES A TRIBE TO BE SELECTED, commands tribe to move to selected tile, costs 1 mana. Tribe will travel in a straight line to destination, seas will block travel and cancel goto.

settle: REQUIRES A TRIBE TO BE SELECTED, on clicking the menu button the selected tribe will form a settlement and no longer wander, takes 1 mana. Settlements can grow crops and have higher populations.

CONTROLS:

Mouse:
When a power is selected, lightning bolt shows whether you have any mana.

leftclick: use current power on tile under mouse.
rightclick: deselect power, defaulting to tribe selection tool
scrollWheel: change range of land-altering power, takes a lot of mana!

Menu buttons:
End Turn: increments the turn counter letting tribes wander and mana increase, press this when you have no more mana left.
Auto End Turn: automatically ends the turn every 1/10th of a second, good way to see how history unfolds! click again to stop.
Settle: REQUIRES A TRIBE TO BE SELECTED tell selected tribe to settle at their current location.
Next Tribe: cycles through all the tribes/settlements in the world.
Goto: REQUIRES A TRIBE TO BE SELECTED tell selected tribe to travel to tile which is clicked after selecting this button

Select Tribe: sets power to default selection tool.
Sink Land: sets power to sink land.
Raise Land: sets power to create lowland.
Raise Hill: sets power to create hills.
Raise Mountain: sets power to create mountains.

-phew!- Hope I didn't miss anything :P Making a God game needs a whole lot of explanation of the controls/gameplay. If it is still confusing try clicking Auto End Turn and just letting the simulation play out (to be honest this is what I have mostly been doing)

Thanks to all the people who comment, I'm overjoyed that people have been interested in my entry :3

Shameless self promotion:
I have a blog where I post programming projects:
http://tangentialtopics.blogspot.co.uk
The ones written in Javascript are playable right on the page :D