Hamburger's etymology

With the summer, comes the hamburgers BBQ parties. The more common is the beef burger but you can try also the veggie burger, the tofu burger, the crab burger, the tuna burger and so on. Our friends from South Carolina claim that Charleston's hamburgers are the best, it's good that's true.
The word "hamburger" derives from Hamburg, Germany's second largest city, from which many immigrants came from in the 19th century.
The Library of Congress has officially declared that Louis lassen of Louis Lunch, a small lunch wagon in New Haven, Connecticut, sold the first hamburger in 1900. But other persons claim for the invention all around the US.