When Ieyasu became shogun in 1603, Edo in turn became the seat of national government and its castle the largest in the world.
Edo Castle was only built once Tokugawa Ieyasu became Shogun.
mnli hypothesis: Edo Castle was only built once Tokugawa Ieyasu became Shogun. premise: When Ieyasu became shogun in 1603, Edo in turn became the seat of national government and its castle the largest in the world.