Charybdis said: Once every generation, so roughly once every ten years. MK1 is indeed the decisive tournament in that regard. We'll get to the Great Kung Lao in due time but there's a lot that happens before him. You need to win ten in a row: otherwise, once Goro beat the Great Kung Lao, Kahn could've just invaded then and there. Click to expand...

You're wrong here. For one realm to be free to merge with another it has to win 10 mortal kombat tournaments in a row. You're right that if whatever streak is broken until the tenth win, the count starts all over. So after Goro killed The Great Kung Lao, he was undefeatable until Liu Kang in MK1, which was supposed to be the 10th tournament Outworld would've won (hence the 500 years after The Great Lao's defeat), which makes it 50 years (a full generation) for the realms to prepare for the next tournament. Also, in MK9 Shao Kahn cconfirms this by saying he'd have to wait another 500 years to be able to merge the realms after Shang's defeat. Invasion is not a problem, by the elder gods standards (again from MK9 story), but the right to merge is what the tournament is for.