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In "Common Sense," a literary bombshell that went through 25 printings in 1776 alone, Thomas Paine blasted King George III as "the royal brute of Britain" and "a full-blooded Nero." And the second part of the Declaration of Independence lists 28 instances of "injuries and usurpations" by which the king sought to establish "absolute tyranny" over the American colonies.

In "The Last King of America," journalist Andrew Roberts, the author of biographies of Napoleon and Winston Churchill, draws on a large cache of documents recently released by the Royal Archives to provide a detailed history of King George's life and 60-year reign. Claiming that George III has been "the most unfairly traduced sovereign" in the history of England, Roberts portrays the king as cultured, intelligent, moral and relatively enlightened.

Although "The Last King of America" effectively refutes Paine, Jefferson and, for that matter, Lin-Manuel Miranda, Roberts is asserting what 20th- and 21st-century historians already know: George III was not a tyrant who lost the American empire; he respected the British Constitution and deferred to Parliament.

Roberts also goes beyond the available evidence to insist that the king's five protracted "maladies," spread over several decades, were caused by a bipolar disorder; suggests that "perceived threats to his honor tipped him over to manic depressions"; and diagnoses overspending by the Prince of Wales, heir to the throne, as "a chronic case of Buying Derangement Syndrome."

"The Last King of America" is at its best when Roberts analyzes how George III navigated issues with personal as well as political implications. A frugal monarch who limited his own annual "allowance," George nonetheless asked Parliament to formally differentiate between his personal property and liabilities and those of the Crown, so that he could provide for his children.

Proud of his unshakable religious faith and sense of duty, the king believed the Catholic Emancipation Act proposed by William Pitt the Younger violated his Coronation Oath to maintain the Anglican Church as "established by law." Although George III abhorred slavery, Roberts points out that he did not endorse abolitionist legislation.

Most important, Roberts examines the role of George III in the evolution of the Constitutional Monarchy in Great Britain between 1760 and 1820. Throughout his reign, the king used patronage — peerages, bishoprics, the annual pensions of former royal officers — as his trump card, to reward allies and "as a veritable blacklist of political opponents." But George III also reinforced a tradition in which the king never vetoed a parliamentary bill, even though he had a constitutional right to do so.

Equally important was the emergence during these years of collective Cabinet responsibility. Ushered in by the increasing size and complexity of government, party loyalty and George III's debilitating illnesses, this approach meant that Cabinet ministers reported directly to the prime minister rather than the king.

The first Hanoverian born on English soil, George III was, indeed, not a tyrant. And he played a role in making it virtually impossible for his successors to be tyrannical.

Glenn C. Altschuler is the Thomas and Dorothy Litwin Professor of American Studies at Cornell University.

The Last King of America: The Misunderstood Reign of George III

By: Andrew Roberts.

Publisher: Penguin Random House, 560 pages,. $40.