Fort Henry, Fort Donelson, Cairo, and the major rivers mattered because they formed a connected transport network. Cairo sat at a critical confluence, while the captured forts opened routes between the Tennessee and Cumberland river systems. Control of those junctions enabled forces and supplies to move between waterways and connected Grant's advance to a larger transport network. This was the logistical background to the Union concentration at Pittsburgh Landing.
Notable Point · 37:04-38:14
Fort Henry and Fort Donelson open the river routes
The capture of river forts and key confluences made the Tennessee, Cumberland, and Mississippi waterways operationally decisive.