When did the belief originate that the USA is capable, or even responsible for solving the ills of the world?
I'm inclined to blame these guys...
Whenever, or however it started, it's a belief that has done more harm to America than it has ever done good.
The US becoming a country of influence and power in the world starts here:
Original six frigates of the United States Navy - Wikipedia
Most countries paid/put up with the Mediterranean pirates. The US did not, defeated them, and showed the world they are a powerful country that will protect their interests by force.
This continues to this day, and "solving the ills of the world" is in their interest.
--------------------------- agree , from the HALLS of 'montezuma to the shores of 'tripoli' . Course , i am only interested in the USA fixing stuff for itself Wheelie .
The First Barbary War (Tripoli) in 1801 was protecting American interests. Barbary pirates were attacking US and other European ships in international waters.
The Mexican American War (Halls of Montezuma) in 1846 could also be argued were in response to attacks on American settlers in Texas and the Western States.
The Spanish American War in 1899 (pictured very inaccurately up above) was the first war where we announced we were going to war to free the Cubans from Spanish oppression. Arguably America's first war of adventure. Although the actual reasons were much more complex, there was no actual threat to the US other than opening markets for US sugar manufacturers to cheap imports.
The American Expeditionary Force in World War I in 1918 was also touted as a war to 'Make the World Safe for Democracy' according to Woodrow Wilson. There was no existential threat to the US from the European War. World War I was simply a war of adventure.