"union flag" -- Wrong! It was the U.S. flag, the Stars and Stripes, the one hated by al-Queda and the Confederates.
Statement of Joseph Lamb: 'I had a Union flag at home and have yet unless they have gotten in and robbed me of it. About the 1st of June, 1861, I had my likeness taken with the Stars and Stripes across my breast.'al-Queda attacked the US and it's flag. The Confederacy did not fire on the US unprovoked, absent the actions of Lincoln war would never have occurred.
From a letter to Simon Cameron from Thomas Hicks: to 'go where and when ordered to defend the Union flag.'
From W. A. Gorman, battle report: 'But a few seconds, however, undeceived both, they displaying the rebel and we the Union flag.'
From Christian Woerner: 'Fort Stedman was again in possession of our troops and the Union flags in it.'