To what extent was WWI an extension of progressivism?
For the most part, America’s participation in WWI was not an extension of Progressivism. There were some ways in which America’s reasons for going to war and its war aims reflected Progressivism. However, there were many ways in which it was all just about self-interest and nationalism.
According to President Wilson, the point of WWI for the United States was to “make the world safe for democracy.” This would have been a goal worthy of the Progressives. The Progressives wanted to make America more democratic so a war for democracy and against tyranny would have appealed to them. In addition, President Wilson’s 14 Points were largely made up of ideas the Progressives would have liked. They would have liked the idea of more democracy and less secrecy. They would have liked the idea of freedom of the seas. They probably would have liked the League of Nations.
However, it is not clear that these noble goals were what propelled the US into war. It seems that nationalism and self-interest had just as much, if not more, to do with it. Part of the reason why the US got into the war was to protect its ability to trade with England and its ability to be sure that England would repay its war debts. This is not very high-minded. The US also got into the war out of anger about things like the Zimmermann Telegram. While this is understandable, it is not particularly noble. These are motives that have more to do with economics and nationalism and revenge.
Thus, it is only partially correct to say that WWI was an extension of Progressivism.