If Noah's Flood were a real event (which it was), it would be an understatement to say it was a significant event in history. Only the eight members of Noah's family who were on the Ark survived the Flood but no doubt they would have told their children about the event. Such a remarkable event would certainly be told and retold generation after generation so that, even centuries after the Flood, everyone in the young world would know about the Flood even if they didn't experience the Flood. We could even predict that every ancient culture would include some account of this Flood in its lore. That's exactly what we find.
The ubiquity of Flood legends isn't just the topic of modern creationists. At least one ancient historian noticed the same thing. In his book, The Antiquities of the Jews, 1st century, Jewish historian, Flavius Josephus penned this paragraph:
Now all the writers of barbarian histories make mention of this flood, and of this ark; among whom is Berossus the Chaldean. For when he was describing the circumstances of the flood, he goes on thus: "It is said, there is still some part of this ship in Armenia, at the mountain of the Cordyaeans; and that some people carry off pieces of the bitumen, which they take away, and use chiefly as amulets, for the averting of mischiefs."--Hieronymus the Egyptian also, who wrote the Phenician antiquities, and Manases, and a great many more, make mention of the same. Nay, Nicholas of Damascus, in his ninety-sixth book, hath a particular relation about them; where he speaks thus: "There is a great mountain in Armenia, over Minyas, called Baris, upon which it is reported, that many who fled at the time of the deluge were saved; and that one who was carried in an ark, came on shore upon the top of it; and that the remains of the timber were a great while preserved. This might be the man about whom Moses the legislator of the Jews wrote.
Josephus had a lot to say about Noah and other characters attested in the Bible. Being Jewish himself, a lot of what he said is simply his retelling of the events from the Bible. What is significant about this passage is that he takes note of how other, non-Jewish historians corroborate details of the Flood revealed in the Bible – namely that there was a great deluge, that a man survived in an Ark, and that the Ark came to rest in the mountains.
Josephus did not know about the Australian aborigines or American Indians. He wasn't familiar with the Aztecs or Incas. I'm not even sure how much he new about the people of the Far east. But he understood that the many Flood legends among the western cultures gave weight to its authenticity. As western civilization made it's way into the entire world, we've discovered many more Flood legends among even remote populations everywhere in the world. What Josephus knew then is even more true today. The number of Flood legends among so many cultures strongly suggests it was a real event in history.