Sure. You can argue just about anything as long as you have facts to back up your statements.
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Of course that can be argued. I hear folks argue the US won the Vietnam conflict, because the US got out with honor. I have an exwife that will argue anything, anytime.
So the US Western Campaign:
Halleck, whom Lincoln said was "little more than a first rate clerk"
Sherman, who waged a total "war", meaning he waged war on civilians, mainly. His march thru the South was hardly a miliary campaign. We credit Osama bin Laden, and now the Taliban, with the same tactics.
US Grant: The first campaign of Vicksburg was a farce. The second campaign was successful, and yes, Grant outsmarted the opposite side. This was 1863. After that, it was a war of attrition, which is not much dependent on leadership. Wars of attrition means many folks die. It is important to remember that in the Vicksburg battle, Grant had 35,000 troops on the battle line, and the Pemberton had 15,000, cut off from supplies. So did leadership win that battle?
Thomas: Frankly, I like Thomas. He was methodical. He was not a gutless cutthroat like Sherman. His historical demise was mainly due to his uneasy relationship with Grant, who did not serve him well. Thomas was not a glory seeker, and in the post-war period, did not write self-serving memoirs as his contemporaries did.
The question. The first of these "successful" campaigns was in May 1863. Before that, the Union routinely faced rout. Is this consistent better leadership?
Leadership is hard to define, and harder to put on a marking scale. For me, Sherman is a shame, and embarassment. We certainly don't train our Army officers to do what he did, and one officer in Vietnam, was put in prison for it (My Lai massacre). It is too early to judge current history actions on that. Thomas did well, but he had the resources, and he used them wisely and efficently. So I give him a positive mark.
Grant, and Thomas, had the advantage in the 1863 of far greater resources to wage battle, and in the final analysis, this is the deciding factor in a war of attrition.
Your argument suffers for lack of consistent evidence. Good luck. As I started this, anything can be argued.