In 1812, taking over Canada was going to be a cakewalk. In 1846 Mexico had supposedly attacked the United States, whereas the opposite was true. Ending slavery was a belated excuse for the Civil War already underway (much like spreading democracy to Iraq), and it is likely that slavery would have ended swiftly had the South been allowed to secede in peace; slaves escaping north would have been escaping to another nation. In 1898 lies about the Spanish that would have made Fox News proud (including lies about the Maine, a ship that was actually blown up from within) helped launch a U.S. war to liberate Cuba, which however occupied Cuba instead of liberating it and occupied the Philippines for good measure, slaughtering people there by the thousands for years.
In 1916 Woodrow Wilson was reelected president on the slogan "He Kept Us Out of War," and proceeded to set up an early version of the White House Iraq Group known as the Committee on Public Information whose mission it was to make Americans hate Germans. The lies (including about the content of the Lusitania) were so effective that they shaped the settlement at the end of the first world war, contributing to the rise of Nazism and the second world war. We entered that second war following an unprovoked attack by the Japanese, unless the threats we had sent the Japanese and the economic sanctions we had imposed on them count as provocation, and ignoring the fact that the U.S. Navy had been given, nine days before Pearl Harbor, orders to shoot down any Japanese planes and blow up Japanese boats it encountered.
The lies of the Cold War, and the Gulf of Tonkin, and the mythical babies taken out of incubators prior to the first Gulf War are still familiar to most Americans. What is unfamiliar to most Americans is the history of truth telling that has accompanied all these warmongering lies. If you want to be informed and inspired by this rich heritage, pick up a copy of "We Who Dared to Say No to War." Here we find Daniel Webster and John Randolph opposing the War of 1812, Henry Clay and Abraham Lincoln Denouncing the Mexican War, Stephen Crane and William Jennings Bryan opposing the war on Cuba and the Philippines, Robert M. La Folette and Helen Keller speaking against World War I, and many, many lesser known prophets for peace. And the endless wars against native Americans are not even included.
"Where is it written in the Constitution," asked Daniel Webster, "in what article or section is it contained, that you may take children from their parents, and parents from their children, and compel them to fight the battles of any war, in which the folly or the wickedness of Government may engage it?"
"[T]aking for true," said Abraham Lincoln, "all the President states as fact, he falls far short of proving his justification; and … would have gone farther with his proof, if it had not been for the small matter, that the truth would not permit him."
While it's not included in the book, I want to add something sung by Pete Seeger:
"When will we ever learn?
"When will we ever learn?"