In possession of that post, we should have kept the entire southern trade of the United States in check

From The Battle of New Orleans: Andrew Jackson and America's First Military Victory by Robert V. Remini.  Page 87.

The day after Jackson’s withdrawal, Christmas, at 11:00 A.M., there was a stir in the British encampment. Salvos were fired into the air and the troops shouted their welcome on “the unexpected arrival” of their new commander, Lieutenant General Sir Edward Michael Pakenham, who had finally caught up with his army. He “was admired and beloved by both officers and men,” said Gleig. On the eve of the Battle of Salamanca during the Peninsular War, Wellington ordered him to lead the 3rd Division and “take the heights in front and drive everything before him.” Pakenham turned to Wellington with the cry “Give me one grasp of that all-conquering hand . . . and I WILL.” And with that pledge he charged forward and completely routed the defending French. Nothing less was now expected of him by both his officers and men. Notwithstanding all the recent hardships these troops had endured, “the city of New Orleans, with its valuable booty of merchandise,” said Captain Cooke, “was craved for by the British to grasp such a prize by a coup de main.”

“It was rumored among the troops that Pakenham had the commission to serve as governor of Louisiana once he captured it and had been promised an earldom when he completed his assignment. It was also believed that a lady waited aboard one of the ships in Lake Borgne and expected to become the general’s wife once the battle had been won.

Not only would the conquest of Louisiana enrich Pakenham but to the English mind it “would have proved beyond all comparison the most valuable acquisition that could be made to the British dominions, throughout the whole western hemisphere,” claimed Gleig. “In possession of that post, we should have kept the entire southern trade of the United States in check; and furnished means of commerce to our own merchants, of incalculable value.”

Lieutenant General Sir Edward Michael Pakenham's sister, Kitty, was Wellington's wife.  They were brothers-in-law.