Rival
Rival (conquest) in the Stellaris encyclopedia: Rivals are officially designated political and strategic adversaries. Declaring a Rival increases Influence generation and can improve relations with other empires that share similar enmities. However, it also worsens diplomatic relations with the rival…
Rival in the game's words
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Rivals are officially designated political and strategic adversaries. Declaring a Rival increases 
Influence generation and can improve relations with other empires that share similar enmities. However, it also worsens diplomatic relations with the rival and may escalate tensions into open conflict.
Rivalries can only be declared against empires of comparable power and are a key tool for asserting dominance, shaping alliances, and justifying hostilities. They are declared in the Contacts tab of the 
Contacts View.
Entries that mention Rival
More in Conquest
Source: common/game_concepts (concept_rival, also concept_rivals) and localisation/english, Stellaris Cygnus v4.5.2 (9776).