The three Practical Bases of Humanity are the "family", the "site", and the "works", in his words.
Little explanation [from me - Bernd]: the family is obvious, the smallest building block of society, the site means settlement essentially, the works (or I could translate it as factory, plant, workshop) is the place where the family members do their work (can be any work, not necessarily physical).
The Preparation for War and the Command of the War sets these practical bases into the service of the wartime goal. The family, the site, and the works are tuned into harmony in the interest of the victory. They provide the moral, mental, and material tools to fight the war.
The war can be won without the fight of the armies, if this harmony of the three Practical Bases of the enemy is disrupted, and they will unable to provide the tools. [I assume examples would be disrupting their morale with propaganda, or forcing their production to be moved from war material, or maybe bombing the infrastructure or workplaces. - Bernd]