Final answer:
The country in question is Portugal, which settled Brazil and had a messianic strain belief called sebastianismo, related to its King Sebastian I. It initiated the Acclamation War to break from union with its Eastern neighbour, starting the rule of the House of Braganza.
Step-by-step explanation:
The country that settled Brazil and was involved in the Treaty of Tordesillas, minimizing colonial conflicts with Spain, is Portugal. Portugal's belief in "sebastianismo" is indeed a messianic strain rooted in the death of its king Sebastian I during a battle against the Saadi dynasty of Morroco in 1578. After a dynastic union with its Eastern neighbour, it broke free through the Acclamation War, ushering in the House of Braganza's rule. Portugal, therefore, plays an enormous role in world history, notably through its colonial endeavors in Brazil.
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