Why the USA has More and Stronger Tornadoes than Anybody Else

Above, the oldest (and IMO, most awesome) photograph of a tornado, taken on August 28th, 1884, about 22 miles southwest of Howard, South Dakota. Photographer unknown. (BTW, this picture was taken less than two months before my grandmother was born.)
Classic "hook echo"; if you see this colorful paisley pattern on your local radar, seek shelter!

Recently, while my son and I were discussing tornado damage in the wake of a deadly tornado in the news, he asked why we almost never hear about tornadoes occurring anywhere but here in the USA.

Good question, I thought. For some reason, most tornadoes on the planet do occur in the continental United States, even though the lower 48 states occupy only about 5% of the world's land area.

But why? How did we luck into all this meteorological melodrama? Is it a Karmic debt for our ancestor's genocide of Native Americans? Nope, they had tornadoes before we got here; we just brought diseases, firearms, alcohol, and a world of hurt, but tornadoes weren't our fault.

It's our unique geography that gives us the edge on damaging tornadoes- the central part of our country hosts a collision of polar air from Canada, tropical air from the Gulf of Mexico, and dry air from the Southwest, which can produce thunderstorms and tornadoes. That's why we have more tornadoes, and stronger ones.

Tornadoes have been reported in every state of the United States, and on every continent except Antarctica, which lacks the necessary contrast between warm and cold air necessary for even thunderstorms to form, much less tornadoes. ...but obviously they have their own challenges there, weatherwise, even without twisters...

TORNADO ZONES.
Simulation indicates the average time between tornadoes rated F-2 or higher ranges from 4,000 years or so (lightest blue) at spots in southeastern Oklahoma—the southern part of Tornado Alley—to more than 2 million years in parts of Nevada (black). Legend indicates intervals in thousands of years.