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On November 17, 1862 advance elements of the Army of Potomac arrive at Fredericksburg. Detailed planning earlier by commanding Union General Burnside had insured that the pontoon bridges necessary to cross the Rappahannock River were present. Maj. Gen Edwin "Bull" Sumner leads his troops into Fredericksburg, pushing out the token Confederate force in the area and occupies Marye's Heights. From there, he covers the the rest of the Army of the Potomac as it crosses the river. Once fully assembled, it will advance towards Richmond.

General Lee orders the Army of Northern Virginia to assemble at the North Anna River to defend Richmond. However, there is political pressure to engage the Union Army as far north as possible to protect Richmond. Furthermore, neither Longstreet's Corps nor Jackson's Corps is in position, both will need to travel many days before they can arrive (IOTL it took Longstreet until Nov 23, and Jackson Nov 26 to move all their men into Fredericksburg).

How long will it take for the Army of the Potomac to cross and attack Richmond? How much time is needed for Lee to assemble his army? Is it possible for the Union to defeat the Confederates in detail? Can Lee stop Burnside in time, or will Richmond fall before the Confederate Army can engage? What will be the results of battle once they do fight?

This seems one of the more plausible PODs in the American Civil War, but I can't remember it being discussed. If the pontoon bridges had been assembled as Burnside planned, then the Army of the Potomac should have crossed without interference and been able to move quickly to Richmond. It's just that people bungled it. What if they hadn't and Burnsides plan worked?
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