Can someone please explain what this statment means when it worded like this? (I tried to figure out what it means, put I keep getting confuse).

That the 1912 election registered, and inspired, fundamental changes in American politics suggests the historical significance of the Progressive Party. ????

Not only was it the driving force of this election, but it remains the most important third party to appear on the American political landscape in the 20th century. ????? Thank you

4 answers

I think it means that by splitting the Republican vote Teddy R. and his Progressive (Bull Moose) party caused the election of a Democrat (Wilson). If he had not entered as a third party we would have gone into World War One with Taft as president and things might have been very different.
This was the only presidential election I can think of where a third party candidate surely and with no doubt changed the outcome of the election profoundly.
Because Roosevelt's third party garnered over 1/4 of the votes shows that the people wanted a lot of features that the Progressives advocated. No other third party has ever won so many votes.

This article discusses it in more depth.

http://www.claremont.org/publications/crb/id.1152/article_detail.asp
I would like to thank you both for your informative answers to my question. I will be sure to check out the article on the web site that you have provided as well. Now I am no longer confused as to what the statement really meant. Thanks again!
You're very welcome.