Which event had the most immediate impact on the native americans who lived on the great plains?

Even though you didn't share any options to choose, I'va got what you need.  The event that had the most immediate impact on the Native Americans who lived on the Great Plains is the hunting of the buffalo to near extinction during the 19th century. I am pretty sure it will help you, but next time post your question properly.

In the late fifteenth century, a major world power that established colonies in the era of old imperialism was france or germany or spain. their colonial activity was mainly limited to america or africa or asia.