The United States of America did have the right to bomb Hamburg. This was done during World War II, and was controlled by the Axis power Germany. Germany attacked the United States first, making any attack against anything that Germany controlled completely rightful and needed to be done from a strategy standpoint.
Hamburg was a German stronghold in World War II. The Axis had openly attacked the United States in its territory. Any response to any of the Axis countries would have been fully permitted. Hamburg is fortunate that an atomic bomb was not dropped on it like Japan. Even that would have been permitted.
By the time Hamburg was bombed in 1943 the end of the war could be seen, Hitler was getting weaker. The bombing of strategic military bases may be justifyable, but not the 45,000 deaths of civilians. America and Britain sunk down to Hitlers level and it was an unjustifiable assault on humanity to burn civilians to death, in a tornado of fire which reached 1000C plus i might add. Google pictures of the devastation, I dare you. Make sure you see the one of the mother with her two dead children burnt to death; oh and the one of the body small boy clinging to a dead man. Sometimes America's patriotism is a bit sickening to be honest.