"Why Do We Pledge Allegiance?"

"The origins of the pledge cannot be understood apart from the “flag movement” of the 1880s, which itself cannot be understood apart from the Civil War. Just as U.S. (that is, Union) flags became more omnipresent during the war, so “loyalty tests” also spread. People suspected of disloyalty were often arrested, eligible for pardon if they submitted to an “oath of allegiance” swearing to “support, protect and defend the Constitution and Government of the United States against all enemies, whether domestic or foreign,” and to “bear true faith, allegiance and loyalty to the same.” Such oral and signed performances were thought to be rehabilitative, making real Americans out of those whose devotion was questionable or had wavered... 

The Pledge of Allegiance was written only with this specific commemoration in mind, though, and with the express goal of driving sales of the Youth’s Companion. It likely would have fallen into obscurity if not for the intense anxiety about immigrants that began to grip many native-born Americans in the 1880s. More than 2.7 million immigrants arrived in the United States in the 1870s, followed by over 5.2 million in the 1880s and another 14.5 million between 1900 and 1919. Bellamy channeled the alarm many felt when he told the NEA in 1892 that “Americanism brings a duty . . . it must be made a force strong enough to touch the immigrant population which is pouring over our country.” Naturally the use of his pledge in public schools was a key component, he contended, for the inculcation of loyalty to the United States... 

While traditions often engender controversy and resistance, probably no U.S. tradition has sparked more opposition than the pledge (and, relatedly, the U.S. motto, “In God We Trust,” adopted around the same time). Not all of this resistance has come from atheists. Indeed, as Ellis notes, “the most important and enduring sources of resistance to the flag salute and the Pledge of Allegiance were religiously based,” coming from religious minorities with objections to the wording of pledges and mottoes and sometimes to the act of saluting or pledging to a flag."

http://bostonreview.net/politics/jack-david-eller-pledge-allegiance

FB: "It likely would have fallen into obscurity if not for the intense anxiety about immigrants that began to grip many native-born Americans in the 1880s."