Imperial Tithe

In the grim darkness of the far future, feudalism is back in style with the Imperial Tithe. No doubt the irony of coming full circle was not lost on the Emperor.

As the Emperor of Mankind was preparing the Great Crusade, he realized that while the Legiones Astartes were excellent as the "spear tip", or vanguard troops, a spear tip still needed a wooden staff to support it. In other words, he needed regular humans to support the Legions. And while Terra alone had billions, the galaxy is a big place, and they couldn't hold every world with just Terran armies. To get around this, the Emperor imposed the Imperial Tithe, a set of payments that a compliant world must pay to the Adeptus Terra for continued protection. For this, an Imperial Commander, or Planetary Governor, must give the Imperium of Man not monetary taxes, but the following:

1. They must pay a tithe of manpower in regiments for the Imperial Army, and later the Imperial Guard.
2. They must provide goods for warfare, such as food, weapons, vehicles, or minerals to make any of the above.
3. They must provide the league of Black Ships with all the unsanctioned-psykers that the planet has managed to capture.

Space Marine homeworlds and Adeptus Mechanicus Forge Worlds are exempt from the regular Imperial Tithe. Instead, Space Marine Chapters must provide a tithe of gene-seed to the Adeptus Terra, which is turned over to the Adeptus Mechanicus for testing to make sure that the Chapter's gene-seed is stable, or be used to make a new Founding of Space Marine Chapters. The Adeptus Mechanicus is free of the manpower and psyker tithes, but must pay with machinery used in warfare.

Monetary taxes are officially separate from the Imperial Tithe, and weren't added until much later when the Emperor retired to Terra and Malcador the Sigillite took over the Council of Terra. Horus Lupercal, Primarch of the Luna Wolves, had concerns that the taxes could end up raising rebellions on planets. In the following ten thousand years, payment of the Imperial Tithe has resulted in planets declaring rebellion, but these in turn are crushed with extreme prejudice.