Hm... How would the battle go? I'm only using the following races:
Dekus
Terminians
Zoras
Gorons
Ikanans
Garo
Gerudo
The Dekus would actually be more likely to start it. Maybe he lost one of his slippers. I dunno.
Anyways, they'd attack the ranch. It's closest (minus Ikana Valley, but he probably thinks everyone's dead there). The Gorman brothers would try to help, to take out their competitors, but the Deku King wouldn't trust them, and would probaby take the Garo Mask as a trophy. The ranch being run by Terminians, Clock Town would retaliate. Seeing as how we know no for sure numbers when it comes to population, I won't use that argument. But, since the Deku have less weaponry and more weaknesses, they'd be defeated quickly, and, being human-ish, they'd probably proceed to the Deku Palace. The scrubs would put up a valiant defense, but they'd be defeated because of the Magic Bean Man, who is himself Terminian, helping soldiers to sneak in.
The Ikanians would be the next to attack probably. Being ever militaristic, Igos would spy a chance to return his kingdom to its former glory and take it. Seeing as how there are near-infinite stalchildren to fight in Hyrule Field, we'll assume the same for Termina. They would have the numbers, and take Clock Town while most of the army is in Woodfall. It helps that much less is known to the Terminians about the Ikanians.
The Terminians would return home after conquering Woodfall to find their home taken, and lay it under siege. The Garo, ever willing to fight the Ikanians, would help them take it back. They would first present themselves to the leaders of the army, who would have taken the Garo Mask as well, and they'd form a tenuos partnership. The battle didn't last long though... The Ikanians would be overthrown at dawn, when they have no power, and be defeated.
There would be some peace then, but the Terminians would have a hard time trusting the Garo, being as invisible and secretive as they are. They would choose a champion who would wear the mask to attack them... But he would fail epically, and the Garo would retaliate, killing most of the army (but sparing most innocent life). They'd also take the mask, so that there would be no chance of one of their order being summoned. After that, they'd probably leave for good.
The remains of the Deku army would go to the Goron for support. A shell of their original numbers, they would explain their cruel treatment at the hands of the Terminians, and, playing on their emotions, would talk them into helping take back Woodfall. When they attack Woodfall (the Gorons being weary, as G-King has yet to convince me), the Terminians would send alert to Clock Town, and the army would go up there in order to stop the attack. Unfortunately for them, almost all Gorons are natural-born fighters, and in their home territory. The Terminians would be defeated. The battle at Woodfall would be won by the Terminians, however, by sending the Gorons to the fish. The Gorons, wanting no more bloodshed, would not attack Clock Town, but they'd allow the remaining Deku to stay in their village.
A rogue group of Terminians, excited by all the battle, would make a deal with the Gerudo, and together attack the Zoras. If they found the overland enterance to their city, they could easily beat most of them on land. The remaining would flee to the Temple. Unfortunately for the Terminians, the Gerudo would stab them in the back, taking it all for themselves.
So, in other words, mostnraces would survive, but Clock Town would be weak, Ikana Castle empty, Woodfall commanded by the Terminians, the Goron turned isolationist, the Deku and Zora turned refugee, and the Garo away. This would leave the Gerudo as prospering the most out of it.
Thoughts?
