It was obviously easy for Pope to occupy Polk at Columbus and for Buell to engage Johnston at Bowling Green with an overwhelming force, while Grant should advance to the assault of Forts Henry and Donelson. Buell, with his army of 40,000 or 50,000 men, might easily have overwhelmed Johnston's 14,000 at Bowling Green. Pope could have so far engaged Polk at Columbus as to prevent the detachment even of a squad from that quarter for Johnston's reinforcement. Grant in the meanwhile could make his advance with 15,000 men--to be reinforced presently to 27,000--and the gunboats, against Forts Henry and Donelson, defended as those works were by no more than 5,500 men. It was Beauregard's urgent advice to withdraw all but garrison forces from Columbus, Bowling Green and Clarksville, and to concentrate an overmastering force for resistance to Grant in front of Fort Donelson. This plan was in some degree acted upon. That is to say enough men were concentrated at the forts to swell the record of Grant's subsequent capture to about 15,000 men, but not enough to defend the position. The plan might have failed had an attempt been made to execute it in its full scope. Attempted by half measures as it was its failure was clearly foreordained. Grant captured the forts and their defending garrisons and made himself master of the two rivers which, next to the Mississippi, were of most vital importance to both sides. After the forts had fallen the occupation of Nashville was quite a matter of course, and equally so was the necessity of the Confederate evacuation of Kentucky and of practically all of Tennessee. Presently after being "kept in" by Halleck Grant was restored to command--though still as a mere volunteer officer under censure and still subject to General Halleck's often paralyzing domination. Grant instantly began, after his habit, to plan a further campaign of damage to the enemies of the Union. One opportunity had been denied to him. He sought another. In the meanwhile his capture of Forts Henry and Donelson had split the Confederate line of defense in two and rendered its further maintenance an utter impossibility. With the Tennessee and Cumberland rivers in Federal possession it was manifestly absurd to think of maintaining a line of defense which those rivers traversed. The success of Grant had completely ended all possibility of coöperation between the eastern and western wings of that defensive line. The forces west of the Tennessee and those east of that river must henceforth act independently and rather hopelessly, or else they must retire to a new line farther south upon which coöperation might be possible.