Foreign interventions constitute a crucial factor in shaping international politics. One significant type of them is third-party interventions in ethnic conflicts. This study focuses on understanding how crucial foreign interventions are in ethnic conflicts, the factors behind these kinds of interventions, and how these factors correspond to the international law framework applying to the case study of the Russian interventions in the Donbas War 2014. The study depends on the national interest approach in analyzing interventions in world politics, the reasons and justifications of the Russian intervention in the insurgency war of Donbas in Ukraine. It summarizes that interventions are mostly to change the balance of power between the parties engaged in the conflict to achieve the national interests of the intervener party, even the humanitarian intervention isn't always altruistic and seeks only humanitarian purposes. Solo interventions can be driven by multiple factors like the existence of ethnic ties between a party of the conflict and an outside party. Also, the diaspora groups can have a significant influence if the right conditions are in their favor. There are other motives for interventions like the irredentism policies and the effect of the political systems of the world's states. The Russian state would not have been able to implement its interventionist policies in the conflict inside Ukraine during the war except because of the presence of a group in the Donbas with ethnic ties to Russia, which justified and facilitated Russia's external intervention and its irredentism policy.