Shortly after, he again journeyed to Philadelphia to the Congress of May 5th, 1775; where he did on his own motion, to the disgust of his Northern associates and the reluctance even of the Southerners, one of the most important and decisive acts of the Revolution,—­induced Congress to adopt the forces in New England as a national army and put George Washington of Virginia at its head, thus engaging the Southern colonies irrevocably in the war and securing the one man who could make it a success.  In 1776 he was a chief agent in carrying a declaration of independence.  He remained in Congress till November, 1777, as head of the War Department, very useful and laborious though making one dreadful mistake:  he was largely responsible for the disastrous policy of ignoring the just claims and decent dignity of the military commanders, which lost the country some of its best officers and led directly to Arnold’s treason.  His reasons, exactly contrary to his wont, were good abstract logic but thorough practical nonsense.

In December, 1777, he was appointed commissioner to France to succeed Silas Deane, and after being chased by an English man-of-war (which he wanted to fight) arrived at Paris in safety.  There he reformed a very bad state of affairs; but thinking it absurd to keep three envoys at one court (Dr. Franklin and Arthur Lee were there before him), he induced Congress to abolish his office, and returned in 1779.  Chosen a delegate to the Massachusetts constitutional convention, he was called away from it to be sent again to France.  There he remained as Franklin’s colleague, detesting and distrusting him and the French foreign minister, Vergennes, embroiling himself with both and earning a cordial return of his warmest dislike from both, till July, 1780.  He then went to Holland as volunteer minister, and in 1782 was formally recognized as from an independent nation.  Meantime Vergennes intrigued with all his might to have Adams recalled, and actually succeeded in so tying his hands that half the advantages of independence would have been lost but for his contumacious persistence.  In the final negotiations for peace, he persisted against his instructions in making the New England fisheries an ultimatum, and saved them.  In 1783 he was commissioned to negotiate a commercial treaty with Great Britain, and in 1785 was made minister to that power.  The wretched state of American affairs under the Confederation made it impossible to obtain any advantages for his country, and the vindictive feeling of the English made his life a purgatory, so that he was glad to come home in 1788.