Which foreign army is thoreau referring to when he says, "conquered by a foreign army"?

Thoreau is referring to the American Army as the Foreign Army

Explanation:

Henry David Thoreau was a writer and he has written an essay on "Civil Disobedience" in his essay Thoreau has criticized the policies and the practice of slavery by the American government.

Henry David Thoreau was sentenced to prison because he refused to pay taxes, because he believed that the money of the taxes was used to fund war.

Henry David Thoreau talked about the American-Mexican war in which the American Army is referred to as the Foreign Army

When Thoreau says, "conquered by a foreign army", by "a foreign army" he is referring to the United States.

Explanation:

Thoreau was influenced by Ralph Waldo Emerson and agreed that social reform began with the individual. In 1846, the United States declared war against Mexico. Thoreau and other Northern critics viewed the war as a plot by Southerners to expand slavery into the Southwest. In protest against slavery, Thoreau had stopped paying his taxes. The local tax collector ignored him first but when Thoreau publicly condemned the U. S. invasion and occupation of Mexico, he decided to act. In July 1846, he was arrested and jailed. But someone anonymously paid his taxes and he was released. This incident motivated Thoreau to write his famous essay, "Civil Disobedience," which stated that it wasn't enough to be just against slavery and the war and a person of conscience had to act. The proclaimed activist manifesto included: "In other words, when a sixth of the population of a nation, which has undertaken to be the refuge of liberty, are slaves, and a whole country [Mexico] is unjustly overrun and conquered by a foreign army ... honest men to rebel and revolutionize."