Treaty of Zaragoza Divides Spheres of Influence in Asia

The Treaty of Zaragoza Divides Spheres of Influence in Asia is introduced through John Blackthorne’s explanation to Toranaga and his court. Its significance lies in the authority it claims for papal decisions: a line drawn across the world is said to place Japan within Portugal’s exclusive sphere, joining religious expansion to commercial control.

The Papal Division

Blackthorne traces the treaty’s background through earlier demarcations. Pope Alexander VI established the first line in 1493; Pope Julius II sanctioned changes to the Treaty of Tordesillas, signed by Spain and Portugal in 1494; and Pope Clement VII sanctioned the Treaty of Zaragoza in 1529. Blackthorne describes the Zaragoza line as a second line of longitude, running across the tip of southern Japan. Under the arrangement as he explains it, Portugal receives exclusive rights to exploit Japan and lands extending from China to Africa, in return for spreading Catholicism.

A Claim of Religious and Commercial Authority

The explanation presents the treaty not simply as a boundary but as a claim that religious authority could allocate distant countries to European powers. The promised spread of Catholicism accompanies the right to exploit those territories, making evangelization and commercial privilege parts of the same arrangement. Blackthorne’s account also distinguishes the division on paper from the struggle over its meaning: Spain and Portugal continue to dispute ownership, particularly because of the wealth of trade with China.

The Japanese Response

Mariko conveys Blackthorne’s explanation to Toranaga, acknowledging that the papal decisions were made when the Christian world, including Blackthorne’s country, was still Catholic. In her account, that unity would make the decisions binding on all nations. Yet she privately questions whether the Pope could have granted Japan to the Portuguese, even as she relays Blackthorne’s insistence that he speaks truthfully. Toranaga asks Lady Kiri for her judgment; she believes Blackthorne is telling the truth but cannot say how to prove it. The scene therefore leaves the treaty’s practical force unresolved while revealing the scale of the foreign claim being made over Japan.