The text is an attempt to analyze the international political situation in the security sector in the context of the crisis which has arisen as a result of the aggressive actions of the Russian Federation in relation to Ukraine: in particular the forcible annexation of the sovereign territory of Ukraine in violation of all the principles and norms of international law and the inspiration of the armed conflict in the eastern regions of Ukraine. For the first time after the end of the World War II aggression has become a fact of reality in European politics. Pan-European and transatlantic security institution – the Organization for Security and Cooperation in Europe – was not sufficiently effective mechanism for crisis management. In two years, the conflict in eastern Ukraine killed about 10 thousand men. The conflict in Eastern Ukraine has radically changed the perception of security in Europe. The problem is that Ukraine, like most of the “new democracies” of Eastern Europe as a result of the transformation processes of the early 90th appeared in a “gray zone” of security. Most of the Eastern European countries overcame the security gap by joining NATO/EU. At the same time, Ukraine remained in the buffer zone and became an object of intense economic, political, informational and military pressure from the Russian Federation. As a result, Ukraine is forced to rely primarily on their own capabilities and the military-industrial potential (not being part of the European collective defense/security), on the other – the international political, economic, informational support from the international community plays a key role in the possibility of Ukraine resist aggression. However, the crisis has led to a certain re-evaluation of existing regional security system: 1) The failure of attempts to build a pan-European security system became obvious; 2) The OSCE in Ukrainian crisis has created a platform for the negotiations and the peace process, but did not provide, at least until now, the mechanism of a real resolution to the crisis; 3) The question of inefficiency, lack of prospects and obsolescence of NATO as a collective security organization may be withdrawn from the agenda; 4) There is an activization of existing and search for new formats of cooperation between European countries in the development and improvement of the international security system in Europe.