It is hard to describe the speed and fervor with which young Americans flocked to the colors. Nothing like it had been seen before, and nothing like it would happen again until the Japanese attack on Pearl Harbor eighty years later. Young men and boys in Northern cities, towns, and hamlets came out to volunteer in amazing numbers. Several state governors telegraphed Washington, D.C., to say that their original regiments were already filled, asking permission to form new ones. These requests were, of course, granted.

Of all the demonstrations for the flag, the Star-Spangled Banner, the single greatest was held in New York City on Saturday, April 20, 1861. Roughly 100,000 persons jammed Union Square in the lower part of Manhattan to hear no fewer than thirteen speakers extol the Union. Those who watched could find no fault with the demonstration. It was not so much anti-Confederate or anti-South as pro-Union. Given that New York City enjoyed a profitable trade relationship with numerous Southern states, the Union Square demonstration was a powerful example of Union sentiment.