Germany did indeed declare war on the US after Pearl Harbor. But the US was already at war with Saddam in 2003. The Gulf War never ended – there was only a ceasefire.
Saddam continued to claim that he had won the Gulf War, that the US had been defeated, as demonstrated, for instance, by the fact that he was still in power while George H.W. Bush had been removed from office.
There are monuments in Iraq celebrating this great victory.
Saddam never complied with the obligations he undertook in order to establish the ceasefire. That should have rendered the ceasefire null and void.
That could have been the path on which Bush proceeded to renewed hostilities. Instead he went to the UN for its blessings and got resolution 1441, in which the entire Security Council agreed that Saddam had not accounted for the WMD he was known to have had. The resolution states that if Saddam did not fulfill his obligations immediately, serious consequences must follow.
And that’s what happened.