This dissertation develops a theory to explain the conditions under which a tripwire force posture deters conventional war. Tripwires have been a common policy tool since the Second World War but the literature largely overlooks the nonnuclear potential of tripwires and underestimates the political power of a tripwire given their relatively low upfront sunk cost. The theory predicts that a small tripwire of military forces deployed to a threatened protégé state ties the hands of the defender state to honor its commitment to the protégé. The tripwire operates via a nationalism mechanism that is universal in the international system and mutually understood by all states. This intelligible signal is credible when paired with the defender’s capacity to escalate by projecting second echelon forces to the protégé’s territory after the outbreak of conventional war. The presence of a tripwire and the capacity to escalate constrains resolved attacker states from selecting a strategy of conventional war by denying its ultimate territorial aims with the impending arrival of second echelon forces. However, the tripwire does not limit the selection of less effective revisionist strategies below the threshold of conventional war. Thus, while tripwires lower the probability of territorial revision by deterring conventional war, motivated attackers still pursue their territorial aims by employing violent and nonviolent strategies that do not ‘trip the wire.’