The United States Congress declared war on Great Britain on this date in 1812. Although trouble between the two nations had been brewing for years, the injustice that captured the heart of Americans—and that was cited as a primary reason for declaring war—was the British practice of impressment, pressing sailors into service. (来源：英语杂志 http://www.EnglishCN.com)

The British claimed the right to board any ship at sea and, if a sailor speaking the King's English could not satisfactorily prove American citizenship, he could be impressed or "forced into naval service."

That sense of the verb impress dates back to the late 16th century; it has an ancestor in the prest that once meant "to enlist by giving pay in advance." Of course, the thousands of American mariners commandeered by the British navy were not paid in advance for serving in His Majesty's Navy.

To Americans, impressment was monstrous; to the British, eager for troops to fight in their war against Napoleonic France, it was a handy way to muster new recruits.

The American perspective on mustering had an element of etymological truth to it. That term for convening or enrolling or calling together troops traveled into English from the Latin verb meaning "to show; point out" but comes ultimately from monstrum, meaning "evil omen; monster; monstrosity."