No, they don't need to get to the connecting road. They needed to come up the Fulton Road from Cartersville.
No, the clock wasn't ticking. If the confederates left Iuka after sundown, then it was no different than what it turned out to be anyways.
No, the separate columns would not be destroyed, because the confederates would suffer from the same problem that Rosecrans suffered from by sending his force up one road - you can only deploy so many troops in battle on a road. And even if a column felt itself hard-pressed, it would just need to fight a delaying action. Make the enemy deploy into a battle formation, then retreat before the fighting starts. Fall back and repeat.
Opting for the connecting road was a flop. Forcing a battle just before sundown was a flop. Leaving the Fulton Road open was a flop. Rosecrans came up with the plan, and then completely messed it up.
First (and I say this respectfully and genuinely), I appreciate that your arguments have become stronger in your third paragraph above and that you are taking a bit more recognition of the relevant record here now in that paragraph. Hopefully you don't reverse on that simply because I stated such. It is a positive thing.
So, the way I see it, there were two central reasons in which the decision was made to not come up the Fulton road. The first was that they had ascertained that forces moving via the Jacinto and Fulton roads could not mutually support one another for most of its length. Second, time was ticking on the day and because they had hit Confederate pickets and been driving them in that morning and into the early afternoon when the determination was made to move up the Jacinto road only, the Army of the West would know at that point that they were coming,
What I then said was that this decision has to be understood from the perspective that the contemporary record reveals clearly that the belief at the time, clearly and repeatedly expressed by Rosecrans, was that the Army of the West could simply pull back via Bear Creek if not seriously pressed and additionally could very likely do so, regardless, if their left wasn't crushed in via the attacks upon them. This is imperative to understand as it severely changes the dynamic of the decision making process as compared to if one doesn't realize this, as was originally the case here on this thread.
Now, in paragraph three you state that divided columns would not have been in severe danger moving up the two roads separately because only so many men can be deployed into battle along a road at one time. There is certainly
some truth to this, however, I would partly disagree that that is really what happened on the Jacinto road insofar as the fighting erupted very quickly and hence Sullivan's brigade simply wasn't fully up into positions by the time that the Confederate attack opened. Same too with the Confederates. They could have delayed the attack had they so chosen to do so and brought more units into the fight from the start, but doing so would have delayed the opening of the attack. It must be recalled though, that they ground along the roads was by no means uniforn. Where the main fighting actually erupted there were a number of fields on both sides of the road. That was the case in some areas along the roads, but not in others. The larger point though is that we know what happened historically. Hamilton's Division barely held on that evening and was supplemented by units from Stanley's Division during the fight. That came about against a Confederate movement down the Jacinto road which initially entailed one infantry brigade (Louis Herbert's), soon joined by a second (John Martin's) and then ultimately joined by the remainder of Little's Division (Elijah Gates and Martin Green's brigades). They
could have moved with the entire Division from the start had they elected to do so and if Federal forces have to make it up the road, rather than the other way around, they have more latitude in determining where to fight,
especially, if they are able to reach the connecting road first. Based on what actually happened, I don't know how can state confidently that there would have been grave risk associated with moving the Hamilton's and Stanley's Divisions up the two roads separately.
However, let's say for the sake of discussion that you are right and such a fighting withdrawal
could have been conducted. How then is that to be communicated with the forces moving via the other road? Via courier, I would presume and by the sound of the firing. It certainly would need to be done quickly enough, lest they not be able to pull back down their road again and move to support their brother forces operating on the other road, or else, that "fighting withdrawal" would be driven back to Cartersville or to the Tuscumbia road down the Jacinto road (to Barnett's Crossroads) and such a route is opened. Furthermore, once you begin to move back down the road to support your brother column, you vacate that road
anyways and at that point there is
no hope left of reaching the connecting road, which needed to be done. The only other option would be to press forward with your other column as rapidly as possible and hope that maybe you can take the enemy in flank, but that is problematic for obvious reasons, as the forces on the other road will still be hard pressed and that road likely to be opened, regardless. So, reaching the crossroads was essential anyway in which you look at it. The risk in moving via both roads was potentially calamitous for the units moving on each road separately. Lastly, if it wasn't sufficiently understood that the attack from Ord's forces was not going to go forward at the previously stated time, then that provides even
further impetus to get there sooner rather than later.
Again, though, in the end, the central point is that it is ultimately irrelevant if you don't make it to the connecting road and beyond from where the attack can be launched. If you don't, it was
highly likely that the Army of the West would escape to the east. Being that they knew that U.S. forces were coming, it was imperative that the Army of the Mississippi get to the connecting road and beyond and launch the attack. Failure to do that most likely results in failure of the operation, whether you move up both roads initially, or not
and no matter what happens on each of those roads. The rest is a discussion
not about whether the plan succeeds or fails, except insofar as that moving via the Jacinto road alone cut desperately needed time out, in a situation in which they didn't have much to spare if this had any hope of actually trapping the Army of the West. Beyond that, it is a discussion
only, or at least
principally, about how best to protect against tail risk (really bad outcomes).
If they don't get to the connecting road and are able to launch the attacks, the plan most likely fails anyways, even if a force on each road would have been sufficient. Being that they
likely wouldn't be due to their size and the reality that forces on each couldn't support one another, we are talking
not about decisions which would induce the plan to fail. We are talking about how best to protect against severe downside risk
in the event that the plan
would fail to accomplish its objectives.
They knew that the U.S. forces were coming. It was known that they would know that they were coming. If the Army of the Mississippi didn't get there that night, the plan had most likely failed. As far as that point is concerned, that they had to push forward in order to get there that night, or else the plan had all but failed, I don't think that there is really much way to controvert that. It is just the clear logical reality on the basis of what is known. So, you have to push on to get there if you can that day, or you essentially give up. Nothing in Rosecrans, nor Grant's, thought process, or communications, would have ever said that if you can potentially get there, don't do so, nor would it have ever said such. If you don't get there, the operation will have all but failed regardless of what is done with the Jacinto and Fulton roads, anyways, as the Army of the West knew that they were coming, at this point. The only way in which the other three paragraph which you wrote above would make any sense is if one were to reject either that that the Confederate Army knew that they were coming, which they did, that they were understood to be able to pull back to the east via Bear Creek, which they were, or that they would pull back if threatened by a major, multi-Army pincer movement which they did know was coming with a river to their back, which they probably would (and were already planning on pulling out of Iuka anyways). There is simply no other way in which they make any logical sense, objectively speaking.