Two countries split the entire unexplored world with a single line on a map

In 1494, Spain and Portugal signed a treaty dividing all lands outside Europe along a north-south meridian in the Atlantic — everything west belonged to Spain, everything east to Portugal. Neither side had any real idea what they were dividing, and it's a large part of why Brazil speaks Portuguese while the rest of Latin America speaks Spanish.

— Kingdoms of Castile and Portugal, Treaty of Tordesillas — 7 June 1494