The Treaty of Lisbon was a pivotal agreement that aimed to clarify and solidify the borders between Spain and Portugal, addressing numerous disputes that had arisen over the years regarding territorial demarcation. This agreement not only provided a formal resolution to these border issues but also resulted in the abolition of Couto Misto, which had functioned as a unique microstate, claiming the status of a self-governing entity from the late Middle Ages. Located in the valleys of the mountains straddling Portugal and Spain, Couto Misto was an area with a mixed cultural heritage and its own specific privileges, much to the interest of historians and travelers alike.

The negotiations for the Treaty of Lisbon were fueled by the desire of both governments to establish clearer and more amicable relations, particularly in light of escalating nationalism and emerging new political ideologies across Europe. By openly discussing and agreeing upon the complexities of their border, both Spain and Portugal sought to foster a more stable diplomatic relationship. This treaty also represented a commitment to international law, where matters of territory could be settled through peaceful negotiations rather than conflict.

The historical context surrounding the treaty was influenced by the political atmosphere of 19th-century Europe, characterized by emerging nation-states and the reformation of borders according to nationalistic ideologies. The inclusion of previously disputed territories into defined national boundaries signaled a change in how nations approached territorial integrity, moving towards a framework where constructive dialogue replaced military confrontation. Consequently, this not only shaped the future of Spain and Portugal but also set a precedent for other European states dealing with similar disputes.