Pope's commission as Major General of volunteers was dated March 21, 1862. (post-war he received regular commission as a brigadier general in 1866, and as major general in 1882).
McDowell's commission as major general of volunteers was dated March 14, 1862, and Banks' as major general of volunteers on May 16, 1861. Fremont's commission as major general of the regular army was dated May 14, 1861.
When the Army of Virginia was organized on June 26, 1862, with Banks', Fremont's and McDowell's commands, General Fremont protested Pope's assignment over him, and was removed to await reassignment, and Sigel eventually took his place. Sigel's commission as major general of volunteers was dated March 21, 1862, same as Popes'.
In 1861 Gen. Pope had served
under Gen. Fremont in Missouri, etc.
However, an April 4, 1862 Public Resolution by the Congress of the United States authorized the President to assign commanders irrespective of seniority between two officers of the same rank...
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To that effect, of the several major generals involved in the formation of the Army of Virginia in June, 1862, President Lincoln selected Major General Pope to command.
Pope's orders were...
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But the Seven Days' battles were actually commencing about Richmond just as these orders were sent...
Of the three corps commanders, had McDowell or Banks had a problem with Pope's assignment to command of the army, they might have requested to be vacated from their commands too. But evidently didn't.
After his relief from his command, Major General Fremont awaited further orders which were not forthcoming before his resignation from the army in 1864 to run for president on the "Radical Democracy Party" ticket. He withdrew from the race, however, a month before the election.
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Following the War, the Public Resolution allowing the President, as commander-in-chief, to assign commands irrespective of seniority, was repealed.
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