Next to Columbus, which the enemy evacuated on March 2, the strongest Confederate fortifications on the Mississippi River were at Island No. 10, about forty miles farther to the south.  To operate against these, he planned an expedition under Brigadier-General Pope to capture the town of New Madrid as a preliminary step.  Columbus and Nashville were almost sure to fall as the result of Donelson.  If now he could bring his two Missouri campaigns into a combination with two swift and strong Tennessee expeditions, while the enemy was in scattered retreat, he could look forward to the speedy capture of Memphis.  But to the realization of such a project, the hesitation and slowness of Buell were a serious hindrance.  That general had indeed started a division under Nelson to Grant’s assistance, but it was not yet in the Cumberland when Donelson surrendered.  Halleck’s demand for enlarged power, therefore, became almost imperative.  He pleaded earnestly with Buell: 

“I have asked the President to make you a major-general.  Come down to the Cumberland and take command.  The battle of the West is to be fought in that vicinity....  There will be no battle at Nashville.”  His telegrams to McClellan were more urgent.  “Give it [the Western Division] to me, and I will split secession in twain in one month.”  And again:  “I must have command of the armies in the West.  Hesitation and delay are losing us the golden opportunity.  Lay this before the President and Secretary of War.  May I assume the command?  Answer quickly.”

But McClellan was in no mood to sacrifice the ambition of his intimate friend and favorite, General Buell, and induced the President to withhold his consent; and while the generals were debating by telegraph, Nelson’s division of the army of Buell moved up the Cumberland and occupied Nashville under the orders of Grant.  Halleck, however, held tenaciously to his views and requests, explaining to McClellan that he himself proposed going to Tennessee: 

“That is now the great strategic line of the western campaign, and I am surprised that General Buell should hesitate to reinforce me.  He was too late at Fort Donelson....  Believe me, General, you make a serious mistake in having three independent commands in the West.  There never will and never can be any cooeperation at the critical moment; all military history proves it.”

This insistence had greater point because of the news received that Curtis, energetically following Price into Arkansas, had won a great Union victory at Pea Ridge, between March 5 and 8, over the united forces of Price and McCulloch, commanded by Van Dorn.  At this juncture, events at Washington, hereafter to be mentioned, caused a reorganization of military commands and President Lincoln’s Special War Order No. 3 consolidated the western departments of Hunter, Halleck, and Buell, as far east as Knoxville, Tennessee, under the title of the Department of the Mississippi, and placed General Halleck in command