The U.S. DID, in fact, bomb Tokyo extensively, just not with an atomic weapon. The US air campaign completely obliterated the city. Incendiary bombs were especially destructive in Japan, where many buildings were constructed using wood. Between 80,000 and 130,000 civilians were killed - more people than in the atomic blasts in Hiroshima and Nagasaki combined. For more: http://www.history.com/this-day-in-history/firebombing-of-tokyo

hi! here are a few more on Tokyo & other alternative atomic bomb targets

• Why didn't the USA bomb Tokyo in WWII?

• Why were the atomic bombs dropped on cities instead of the emperor's palace in Tokyo?

• Was there any thought given in 1945 of using the atomic bombs on a military target instead of a city? - already in /u/OldWorldGlory's post

• What was the next city the USA planned on using an atomic bomb on after Hiroshima and Nagasaki?

more on Tokyo (non-atomic bombing)

• Which cities other than Nagasaki and Hiroshima had the most catastrophic bombings in the Second World War?

You might be interested in some previous threads on Tokyo and atomic bomb targeting during World War II:

• Which cities other than Nagasaki and Hiroshima had the most catastrophic bombings in the Second World War? - 4 comments, over 1 year old.
• The commenters go over the details of several large scale firebombings done by the Allies during the Second World War and include some books and links to read.
• Was there any thought given in 1945 of using the atomic bombs on a military target instead of a city? - 7 comments, over 1 year old.
• The commenters here link several primary sources on nuclear targeting work done during the war with context added that you may find illuminating.
• During the decision to create the atomic bomb, was there any thought of creating 'smart bombs' instead, to reduce civilian casualties? - 4 comments, over 1 year old.
• One commenter here uses primary source documents which specifically discuss the pros and cons of attacking various cities with nuclear weapons.
• AMA: I am Alex Wellerstein, historian of science, creator of the NUKEMAP — ask me anything about the history of nuclear weapons - 214 comments, over 1 year old.
• This is by its nature a mostly Cold War focused thread but there are a few questions and answers about the first nuclear weapons buried inside.

They did. It's a widely known fact that the US firebombed Tokyo. If you're referring to nuclear weapons, it's widely accepted that Hiroshima and Nagasaki were chosen to give the impression that if Japan did not surrender, Tokyo would be next.