Thanks for your help. I believe it was the Americans who declared war on Britain. (This question is a little difficult to qualify in so far as it has rarely happened to America and does it count if you counter-declare war rather than make the initial declaration.) It could simply be Hitler
Another complication to this question is the question does a head of state actually declare war? In recent history has it not been a branch, or branches, of the government which actually makes a declaration of war?
According to our friends at Wikipedia, "...in 1801, Yussif Karamanli, the Pasha (or Bashaw) of Tripoli... declared war on the U.S. by cutting down the flagpole front of the U.S. Consulate in Morocco, Algiers, and Tunis...
Thus began The First Barbary War (1801�1805)... Yussif Karamanli signed a treaty ending hostilities on June 10, 1805...
Sounds as if Clanad is correct, though I am unclear whether Tripoli was a state - it appears to have been an Ottoman province, around the current Libyan capital. (Incidentally, Clanad, is this the Tripoli whose shores are sung about along with the halls of Montezuma?)
Tripoli was the subject of the interest of the US Marines.They were in the area to deal with pirates ( that's Fox News' version, put out in the light of recent piracy stories !). In fact they landed to reinstate the ruler of the Barbary state, who had been deposed by one of his relatives.They won the consequent first battle of 'The Barbary War' in 1805, at a place called Derna, near Tripoli.