The thesis proves that around the establishment of the European Union army, we can infer two opposing narratives in European Union’s media and political space and that both meet the conditions to be called a securitization. The first narrative (positive securitization) that the thesis analyses argues that the precarious the security situation in and around Europe could become an existential threat to the society of European Union (EU) and European identity because of the paucity of the EU army. The second narrative (negative securitization) that the thesis analyses interprets the establishment of the EU army as an existential threat to the North Atlantic Alliance (NATO) and the sovereignty of EU member states. Securitization is defined through the Theory of Securitisation by the scientists belonging to Copenhagen School (Barry Buzan, Ole Wæver and Jaap de Wilde) as a speech act by which an actor (securitizing actor) presents a specific issue, until then only politicised in the political or public space, as an existential threat to the referent object that requires extraordinary measures. For a speech act to be an act of securitization and not just an attempt of securitisation, public (or a target group) needs to accept the speech as such. Thus, the Theory of Securitization affirms that the chosen narratives are acts of securitizations through discourse analysis and public opinion analysis. Elements of securitization are before mentioned securitization actor, referent object and public, as well as functional actors, which indirectly affect security decisions by lobbing or directing the securitization actors, and context, as a speech act cannot be an independent factor in the securitization process but is dependent on historical, political, societal, economic, geographic, and other variables. The principal difference between Theory of Securitisation and the mainstream security theories: Traditional Security Studies (TSS) and Critical Security Studies (CSS), is that Theory of Securitization is not concerned if the issue that a speech act wants to present as a security issue, really is a security issue, but how a speech act presents the issue as a security issue. Unlike the Theory of Securitisation, TSS is a realistic security theory that examines is the issue a real security threat while CSS is a constructive security theory that examines the reality of security threat. Both, TSS and CSS, analyze already present security threat, while Theory of Securitisation analyses the creation of the security threat. Positive securitisation, the precarious security situation in and around Europe that could become an existential threat to the society of the EU because of the paucity of the EU army, is securitised by European federalists headed by European Commission President Jean-Claude Juncker and HR/VP Federica Mogherini. Referent objects that are in urgent need of protection are the EU society and the European identity (values and principles) that are in the existential threat of Russia and uncertain security situation in the immediate neighbourhood of the EU. As a solution for the existential threat, securitising actors impose the establishment of the EU army. Functional actors of positive securitisation are stakeholders in the European defence industry who have a purely economic reason for the backing of positive securitisation, and European elite which advocates the federalisation of the European Union. The prime public, core target group, for the positive securitisation should be the Heads of 28 EU member states who make decisions concerning Common Security Defence Policy (CSDP). As the decisions concerning CSDP must be unanimous, and some member states, mostly United Kingdom (UK), steadily use the instrument of veto to block further development of the CSDP, the thesis assumes that the securitising actors of positive securitisation decided to expand the target group for their securitisation onto European Union society as a whole. Reasons behind the expansion of the target public, which thus makes the whole society of the European Union a the public is a pressure onto the Heads of EU member states since the citizens of the EU have a very favourable opinion about the further development of the CSDP and mostly positive opinion regarding the establishment of the EU army. Negative securitisation, which interprets the establishment of the EU army as an existential a threat to the NATO and the sovereignty of EU member states, is a complex form of securitisation. Instead of one securitising actor or one group of securitising actors with the same motive (European federalist with Juncker as champion in positive securitisation), negative securitisation is securitised by several securitising actors without the leading champion with sometimes the same and sometimes different motives: Eurosceptics, NATO, decision-makers in the United Kingdom, the United States (US) and Russia. Furthermore, negative securitisation accumulates the referent objects that are in urgent need of protection: the sovereignty of the EU member states and the survival of the NATO alliance. The only element of the negative securitisation that is unambiguous is the existential threat from the establishment of the EU army whose establishment would take away the national armies, i.e. the sovereignty of the EU member states and made the NATO alliance vulnerable. Hence, for the sake of simplicity of understanding the elements of negative securitisation and their synergy, the thesis uses the Classical Security Complex Theory (CSCT) for the proper consideration of the patterns of the security connections. Using discourse analysis of the speech acts and official documents the thesis shows how the decision-makers in the US (regardless of their political affiliation) securitise the establishment of the EU army as an existential threat to NATO and future of Atlantic security cooperation. Same is evident with the NATO as a securitising actor. The decision-makers in the UK (mostly conservatives) securitise the establishment of the EU army and further development of CSDP as an existential threat to the national sovereignty of EU member states. Russia too securitises the establishment of the EU army as an existential threat to the national sovereignty of EU member states but does the deed backstage financially supporting nationalist and Eurosceptic EU parties and via cyber-attacks and disinformation campaign. Functional actors of negative securitisation are stakeholders in the non-EU defence industry and other industries which prosper due to unstable global security situation, private military organisations, non-independent think thanks, etc. The public for the negative securitisation is the Eurosceptic part of the EU society, but the core target group are the citizens of the UK. Securitising actors of the negative securitisation narrowed the public of their securitisation for the same reason why the securitising actors of the positive securitisation broaden theirs – decisions concerning CSDP must be unanimous. Consequently, the securitising actors of the negative securitisation to be successful in their securitisation need to persuade only citizens of the UK that their narrative is correct. As already mentioned, the Theory of Securitisation analyses the creation of the security threat, so very important for the understanding of the results of discourse analysis is the context behind the construction of the securitisation. In the case of the securitisations analysed in the thesis, the contexts of both narratives have foundations in the conflict between neorealist and neoliberal doctrines in foreign politics, different security strategies of the countries, and change in a global security system, as well as historical, political, societal, economic, geographic and other variables. No EU member state can be a superpower on its own in today’s world. This notion and aim to hinder the possibility of another armed conflict in Europe prompted the creation of the Union. After more than 60 years of enlargement and integration, the EU is an economic superpower. Nevertheless, to protect its economic superiority as well as to impose its doctrine in foreign politics and expand its multilateral security strategy, the EU needs to be and defence union. This idea is not a new one but exists and was attempted to be implemented from the beginning of the EU existence. The securitising actors of the positive securitisation believe that with the establishment of the EU army, the EU can keep the US hegemony in the global security system and the Russian renewal of bloc-system aspirations under control. Some securitising actors of the positive securitisation also believe that the further integration of the EU is necessary to prevent the disintegration. Above all, is the strong desire of the EU elite for the federation of the EU. Expectedly, not least because of the postulate of the security dilemma, the US and Russia are afraid of the military-strong EU which could change the current global security system, while the UK believes that with the strengthening of the EU its military and political strength will wane or disappear. As the UK is the EU member state and its citizens are the most Eurosceptic the public in the EU, both and the US and Russia focused most of their securitisation’s efforts toward the UK's citizens. The US also uses the UK as a tool of disruption in the EU – it's right to veto decisions about the further development of CSDP, integration of the EU in the defence field and the establishment of the EU army. The thesis hypothesises that the two opposed narratives that the thesis considers to be securitisations have generated the status quo in the development of CSDP. Through the discourse analysis of speech acts and the official documents of securitising actors of both narratives as well as analysis of the acceptance of narratives by the audience (public opinion analysis), the thesis positively answers the research question: Is the securitisation theory usable the instrument in the effort to implement/block more effective EU integration?