True rogues are more common in fiction than in life. That’s because a rogue has to be charming, persuasive, duplicitous, imaginative and opportunistic all at the same time. It’s easier to invent such a person than to be one. Aaron Burr managed it, and David O. Stewart’s “American Emperor” explains how. Merely a talented lawyer and ambitious politician up to the age of 48, Burr had to change course after he killed Alexander Hamilton on the dueling grounds of Weehawken, N.J., in July 1804. Duels had taken on a distinctive cast in the new nation, where three-quarters of them were inspired by politics. There was even a congressional dueling spot in Bladensburg, Md. With politics no longer the preserve of the elite, partisan insults went public, inciting challenges such as Burr’s to Hamilton. New York and New Jersey indicted Burr for murder, halting his law practice there. He was in his last year as vice president, and his political career was running out of steam. Put on the Republican ticket with Thomas Jefferson in 1800 because he could deliver New York, Burr had lost all credit with his Republican colleagues after conniving with Federalists when a tied vote in the Electoral College shifted the choice of the president to the House of Representatives, where Jefferson was the victor. Burr’s roguish qualities manifested themselves when his term ended. He decided to go west and see if he could detach the frontier states of Kentucky, Tennessee and Ohio from the union, or exploit the discontent of New Orleans creoles newly incorporated into the United States by the Louisiana Purchase, or perhaps raise an army and wage war on Spain. As these possibilities suggest, the United States was anything but settled 25 years after independence. Stewart does a fine job of conveying the restlessness, resentment and unmoored fancies that prevailed among the men who had gone west to make their fortune while France, England and Spain continued to jockey for position in the New World. “American Emperor” delivers a colorful narrative of the schemes that carried Burr from one reckless venture to the next. Of inestimable value in following his frenzied recruitment of allies are Stewart’s thumbnail sketches of “Leading Characters” at the front of the book. Stewart gets his title from Burr’s plan to invade Mexico and set himself up as its liberator. Jefferson’s insistence on pursuing peace with Spain pushed Burr to turn to England and then France for backing. The former vice president could still meet with important people, eventually getting an interview with Napoleon in Paris. As Burr pursued his bellicose projects, he was both secretive and indiscreet. You get the impression that just talking about his grandiose designs gave him pleasure. After a tour of the frontier, he teamed up with an Irish immigrant, Harman Blennerhassett, who offered funds and his island in the middle of the Ohio River as a site for collecting food, weapons and volunteers for a future assault on Spanish-controlled Mexico.