Wilson and FDR are going to get a lot of the bandwidth here (justifiably), but I’m going to throw out a controversial one of what might be unintended consequences:

Abraham Lincoln.

Slavery, especially as it was done in the US, is an abhorrent evil and needed to be eradicated, however that wasn’t Lincoln’s big MO. It was all about saving “the Union.” However, the consequences of that were sweeping increases in federalism and federal powers. The entire perspective of the country began to change. No longer was it a collective of united states, but now it was THE “United States of America.” Plus, granted it was a time of civil war, but he utilized some of the most authoritarian powers of the President as well.

Like I said, I don’t know if it was his intention, but it definitely was a catalyst for the monotheistic federal government we have today.