War & Rumours of War: Matthew Yglesias is 100% correct here. And I would put it much more strongly. It is not “[un]clear… that Hooker needed to withdraw and abandon the offensive”. It is, rather, clear that Hooker had every reason to continue the offensive. At the very least it would attrit Lee, and it might have led to his defeat in detail:
Matthew Yglesias: : ‘Robert E Lee’s hype as a military genius has… its] foundation in reality… from his success at Chancellorsville…. 60,000 men faced down the 108,000-strong Army of the Potomac… with an additional force of 28,000 more… at Fredericksburg under… Sedgwick. Lee won decisively… with some very unusual tactics — dividing his force twice in the face of a numerically superior opponent…. Admirers call this “Lee’s perfect battle,” and certainly it’s hard to argue with success. But it’s also hard not to look at it as involving a series of significant errors by Union general Joseph Hooker…. Even with all the blunders, it’s not actually clear to me that Hooker needed to withdraw and abandon the offensive. The Union lost more men, but the Confederacy lost a larger proportion of their army… <slowboring.com/p/matts-…>
The Union army suffered 17,000 casualties at Chancellorsville; the Confederates 13,000—15% of those engaged in total. Compare to 25% at Antietam in 1862, 31% at Gettysburg in 1863, and 28% at the Wilderness and Spotsylvania in 1864. In my view, it is very clear that Hooker did not need to withdraw, and that he did withdraw because he massively overestimated the size of the Confederate army—they had, after all, attacked him from pretty much every possible direction except from due north. Both the Seven Days’ Battles and Chancellorsville were victories won not on the ground, where things were inconclusive, but in the mind of the Union commander.
And I do think Matt gets one thing wrong here: the real foundation for Lee’s military genius is Second Bull Run, and Longstreet’s flank attack there. That was the battle where Lee won a major victory on the ground, and not in the mind of the Union commander.
