Burgers were invented in America.
Now sure, the Hamburger is named after Hamburg in Germany. However, the German version is actually the Hamburg steak. In other words, the meat patty. And a patty does not a burger make.
America was the country that put the bun on the hamburger. This, in drag’s opinion, is when the Hamburg steak became the “burger”. A new word, losing the ham and becoming what would be translated from German as “The people’s meal”. An apt description for the American burger.
I believe the oldest recipe for a burger was from the roman empire. It was sold by food carts/street vendors, and was a version of fast food.
It was ground up meat, mixed with spices, cooked on a hot plate, and served between 2 bits of bread/roll. That sounds quite burger like to me.