What was the most significant event on May 21 during the U.S. Civil War?

Saturday, May 21, 1864: Horace Porter, an aide-de-camp to Gen. Grant, writes his own impressions of the Battle of Spotsylvania Court House, particularly of the fight at the Bloody Angle on May 12: “The opposing flags were in places thrust against each another, and muskets were fired with muzzle against muzzle. Skulls were crushed with clubbed muskets, and men stabbed to death with swords and bayonets thrust between the logs in the parapet which separated the combatants. Wild cheers, savage yells, and frantic shrieks rose above the sighing of the wind and the pattering of the rain, and formed a demoniacal accompaniment to the booming of the guns as they hurled their missiles of death into the contending ranks. Even the darkness of night and the pitiless storm failed to stop the fierce contest, and the deadly strife did not cease till after midnight.”
“On May 20 [1861], the Confederate Congress voted to move the government to Richmond...With that, Virginia's capital had become the very symbol of the Confederacy, and the ultimate prize in a bloody war.”--Ernest B. Furgurson, Ashes of Glory
“When the Confederate government moved from Montgomery, Alabama to Richmond, Virginia, the quiet, prosperous Virginia state capital was transformed into a noisy, crowded metropolis that, as Furgurson notes, was capital, military headquarters, transportation hub, industrial heart, prison, and hospital center of the Confederacy. It was also a target for the Union army. In fact, the effort for both the Union and the Confederate armies during much of the Civil War in the east focused on capturing or threatening the enemy's capital city. Since the Union capital--Washington D.C.--and the Confederate capital--Richmond--were located a mere 100 miles apart, much of the fighting raged between these two cities. Washington was never seriously threatened by Southern forces, but Richmond experienced more than its share of alarms and battles.”
Pictures: 1862 stonewall Jackson valley campaign map battle; 1864 photographer Timothy O'Sullivan shot on May 21, 1864, at Massaponax Church. The Army of the Potomac is leaving Spotsylvania Court House behind; 1864 Salem Church, being used as a Civil War field hospital for Spotsylvania battle; xx
Since RallyPoint truncates survey selection text I am posting events that were not included and then the full text of each survey choice below:
A. Wednesday, May 21, 1862: The Union army under Maj. Gen. Nathaniel P. Banks, numbering about 9,000 men, was concentrated in the vicinity of Strasburg, Virginia, with two companies of infantry at Buckton Depot. Col. John R. Kenly commanded 1,063 men and two guns at Front Royal. Confederate cavalry under Col. Turner Ashby confronted Banks near Strasburg, but then withdrew to join Stonewall Jackson’s army, which crossed Massanutten Mountain via New Market Gap. Stonewall was marching to join forces with CSA Maj Gen Richard S Ewell at Luray, Virginia.
B. Thursday, May 21 1863: Battle of Plains Store, Springfield Road, Louisiana. Union victory and the last Confederate escape route from Port Hudson was closed. Early in the morning, Major General Christopher C. Augur's Union division advanced from Baton Rouge toward the intersection of Plains Store and Bayou Sara roads on the way to secure a landing, on the river, for Major General Nathaniel Banks. Colonel Benjamin H. Grierson's cavalry, in the lead, encountered Confederate forces under the command of CSA Colonel Frank P. Powers and skirmishing ensued. As the morning progressed the Union infantry approached the crossroads and came under fire, bringing on a general engagement. At noon, CSA Colonel William R. Miles set out for Plains Store with Confederate reinforcements. By the time that Miles arrived in the area late in the day, the fighting had ceased, the Rebel forces had retreated, and the Federals were preparing camps for the night. Miles attacked the Union forces and, at first, drove them, but they regrouped and counterattacked. Miles could not stand against the overwhelming Union force and retired into the Port Hudson perimeter. The battle ended, and the last Confederate escape route from Port Hudson was closed.
Forces Engaged: 1st Division, XIX Army Corps and Cavalry Brigade [US]; small combined infantry, artillery, and cavalry force [CS]
Estimated Casualties: 250 total (US 150; CS 100)
C. Saturday, May 21, 1864 Battle of Spotsylvania, Virginia Day 13: On May 21st, the Union army finally disengaged from the Confederates and traveled southwest to where the Battle of North Anna would take place. This battle has been one of the bloodiest battles in the War. It has been the longest battle in the war, being 14 days of constant engagement between the two armies. Going into the battle, Grant has 100,000 troops under his active command, and Lee has no more than 52,000. But a total of almost 32,000 casualties makes this one of the costliest battles for either side.
By this evening, Grant finally gets Hancock’s flank march going, as he heads southward. But Lee does not take the bait: instead, tomorrow he marches a parallel course to shadow the Federals and hopefully block them from their next target. Confederate Victory.
Losses Killed Wounded Captured/Missing Total
U.S. 2,725 13,416 2,258 18,399
C.S. 1,515 5,414 5,758 12,687
1. Tuesday, May 21, 1861: Missouri declares its neutrality in the Civil War
http://blueandgraytrail.com/year/186105
2. Tuesday, May 21, 1861: Sterling Price signs an agreement with William Harney, essentially handing Missouri over to federal forces.
http://blueandgraytrail.com/year/186105
3. Tuesday, May 21, 1861: “On May 20 [1861], the Confederate Congress voted to move the government to Richmond...With that, Virginia's capital had become the very symbol of the Confederacy, and the ultimate prize in a bloody war.”--Ernest B. Furgurson, Ashes of Glory
“When the Confederate government moved from Montgomery, Alabama to Richmond, Virginia, the quiet, prosperous Virginia state capital was transformed into a noisy, crowded metropolis that, as Furgurson notes, was capital, military headquarters, transportation hub, industrial heart, prison, and hospital center of the Confederacy. It was also a target for the Union army. In fact, the effort for both the Union and the Confederate armies during much of the Civil War in the east focused on capturing or threatening the enemy's capital city. Since the Union capital--Washington D.C.--and the Confederate capital--Richmond--were located a mere 100 miles apart, much of the fighting raged between these two cities. Washington was never seriously threatened by Southern forces, but Richmond experienced more than its share of alarms and battles.”
http://www.civilwar.org/education/history/warfare-and-logistics/warfare/richmond.html
4. Wednesday, May 21, 1862: New Market, Va.: My dear Wife, The Yankeys have apparently abandoned the [Shenandoah] Valley & seem to be on the march for Richmond. We are at New Market, Va and have just got here & the entire army has taken the road towards Luray & will cross into Madison & probably go by Frescatti [Frascati, the ancestral home of Warren’s wife Virginia ‘Jennie’ Watson Magruder which is located a few miles north of Gordonsville]. You will therefore not leave home until you hear futher [sic].
I am most affectionately; E. T. H Warren [Edward Tiffin Harrison Warren, Colonel, 10th VA Infantry]
http://150yearsagotoday.blogspot.com/2012/05/1862-may-21-new-market-va.html
5. Thursday, May 21 1863 --- The Richmond Daily Dispatch publishes this editorial, offering an overly optimistic picture of what is happening to Confederate fortunes on the Mississippi: Affairs at Vicksburg. We present under our telegraphic head all the news we have from this important point. It is natural that much anxiety should be felt with reference to the defence of this place, and, without presuming to know more than others, we predict that all will be well there on the great day of trial of strength between the two armies. There is nothing, in our judgment, in the recent repulse of Gen. Pemberton to lead to the belief that there is any danger of the fall, immediate or remote, of Vicksburg. We are informed from various sources that our forces within the entrenchments, extending from the city as far back as the Big Black, have a supply of provisions sufficient to subsist them for four months.
In the late fight only a portion of our forces were engaged, and Gen. Johnston, who is now in command of all the forces employed for the protection of the place, with the reinforcements sent to his aid, had not arrived in time to participate in the struggle. His dispatch the day subsequent to the fight was dated forty miles from the scene of the engagement. From all we can gather we are decidedly hopeful as to the final issue.|
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=May+21%2C+1863
6. Saturday, May 21, 1864 --- Horace Porter, an aide-de-camp to Gen. Grant, writes his own impressions of the Battle of Spotsylvania Court House, particularly of the fight at the Bloody Angle on May 12: The opposing flags were in places thrust against each another, and muskets were fired with muzzle against muzzle. Skulls were crushed with clubbed muskets, and men stabbed to death with swords and bayonets thrust between the logs in the parapet which separated the combatants. Wild cheers, savage yells, and frantic shrieks rose above the sighing of the wind and the pattering of the rain, and formed a demoniacal accompaniment to the booming of the guns as they hurled their missiles of death into the contending ranks. Even the darkness of night and the pitiless storm failed to stop the fierce contest, and the deadly strife did not cease till after midnight.
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=May+21%2C+1864
7. May 21, 1868: Republican Convention nominates Ulysses S. Grant to run for President of the United States and Schuyler Colfax as Vice-president
http://blueandgraytrail.com/year/1868
8. Tuesday, May 21, 1861: Confederate Congress votes to move its capital from Montgomery, Alabama to Richmond, Virginia
http://blueandgraytrail.com/year/186105
A Wednesday, May 21, 1862: The Union army under Maj. Gen. Nathaniel P. Banks, numbering about 9,000 men, was concentrated in the vicinity of Strasburg, Virginia, with two companies of infantry at Buckton Depot. Col. John R. Kenly commanded 1,063 men and two guns at Front Royal. Confederate cavalry under Col. Turner Ashby confronted Banks near Strasburg, but then withdrew to join the main army, which crossed Massanutten Mountain via New Market Gap to reach Luray, Virginia.
https://en.wikipedia.org/wiki/Battle_of_Front_Royal
B Thursday, May 21 1863: Battle of Plains Store, Springfield Road, Louisiana. Union victory and the last Confederate escape route from Port Hudson was closed. Early in the morning, Major General Christopher C. Augur's Union division advanced from Baton Rouge toward the intersection of Plains Store and Bayou Sara roads on the way to secure a landing, on the river, for Major General Nathaniel Banks. Colonel Benjamin H. Grierson's cavalry, in the lead, encountered Confederate forces under the command of CSA Colonel Frank P. Powers and skirmishing ensued. As the morning progressed the Union infantry approached the crossroads and came under fire, bringing on a general engagement. At noon, CSA Colonel William R. Miles set out for Plains Store with Confederate reinforcements. By the time that Miles arrived in the area late in the day, the fighting had ceased, the Rebel forces had retreated, and the Federals were preparing camps for the night. Miles attacked the Union forces and, at first, drove them, but they regrouped and counterattacked. Miles could not stand against the overwhelming Union force and retired into the Port Hudson perimeter. The battle ended, and the last Confederate escape route from Port Hudson was closed.
Forces Engaged: 1st Division, XIX Army Corps and Cavalry Brigade [US]; small combined infantry, artillery, and cavalry force [CS]
Estimated Casualties: 250 total (US 150; CS 100)
http://americancivilwar.com/statepic/la/la009.html
B+ Thursday, May 21 1863 --- Battle of Plains Store, Louisiana -- Gen. Nathaniel Banks and the Army of the Gulf, after campaigning in southern Louisiana over the last couple of months, converges on Port Hudson from several directions. In addition, reinforcements come from New Orleans. Banks has 30,000 opposing Confederate Gen. Franklin Gardner’s 7,500. On this date, Gen. Christopher Auger, with a Federal division, drives back advance Rebel forces north of Port Hudson---but only after six hours of delay and charge and countercharge. Thus, Auger creates a staging area north of the Confederate bastion, and cutting off the Rebels’ last escape route. The Siege of Port Hudson is under way. Union Victory.
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=May+21%2C+1863
C Saturday, May 21, 1864 --- Battle of Spotsylvania, Day 13: By this evening, Grant finally gets Hancock’s flank march going, as he heads southward. But Lee does not take the bait: instead, tomorrow he marches a parallel course to shadow the Federals and hopefully block them from their next target.
This battle has been one of the bloodiest battles in the War. It has been the longest battle in the war, being 14 days of constant engagement between the two armies. Going into the battle, Grant has 100,000 troops under his active command, and Lee has no more than 52,000. But a total of almost 32,000 casualties makes this one of the most costly of battles for either side. Confederate Victory.
Losses Killed Wounded Captured/Missing Total
U.S. 2,725 13,416 2,258 18,399
C.S. 1,515 5,414 5,758 12,687
http://civilwarsesquicentdaily-wolfshield.blogspot.com/search?q=May+21%2C+1864
C+ Saturday, May 21, 1864 --- Battle of Spotsylvania, Day 13: On May 21st, the Union army finally disengaged from the Confederates and traveled southwest to where the Battle of North Anna would take place.
http://totallyhistory.com/battle-of-spotsylvania-court-house/
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LTC Stephen F. thank you for the well conceived most significant event on May 21 during the U.S. Civil War? I am going to go with:1862: The Union army under Maj. Gen. Nathaniel P. Banks, numbering about 9,000 men, was concentrated in the vicinity of Strasburg, Virginia, with two companies of infantry at Buckton Depot. Col. John R. Kenly commanded 1,063 men and two guns at Front Roya --Huge battle of epic proportion IMO.

Excellent piece today! The Confederates fought well but the Union's mass overwhelmed their resources.