Cold War ended with the fall of Berlin Wall in November 1989 and the dissolution of the Union of Soviet Socialist Republics (USSR) in December 1991.

Security is a contested concept not because it is difficult to define as a word, but because it refers to a situation in which there are numerous referent objects and actors being in a constant interaction.

There were two reasons. First was the end of the bipolar international security system. It was assumed in the early 1990s that relevance of the system level great power rivalry was reduced, if not totally lost, in the explanation of interna-tional security issues. Second was the rise of security problems around the world
caused not essentially by great power rivalry, but by domestic state failures and regional inter-state disagreements.

Realism provides a wide range of theoretical tools on security including its both Classical and Neorealist versions. Although many scholars argue that the time of Realism should be left to the Cold War era as it was then the dominant explana-tory tool, it is, in fact, not so, for two reasons. First, the Realism has still been offering theoretical and practical tools on state security, war and peace. Second, almost all of the rest of the theories on security have been in an effort to develop their perspectives on the critiques of Realism.

States are the most important units/ actors in international politics. (Terriff et al., 1999: 33-34). Inter-state actions create international system in which other actors, such as international institutions, cannot play as important role as states can. Thus, other actors rather than states have a secondary place in internation-al system.

They think that the states are similar to individuals in that they are essentially unspoiled, unselfish, and conjunctive. States display this positive behavior in numerous ways, such as politics and economics, in wider scope of international politics.

For the Liberalists, international institutions are other key entities in having and further boosting international security. International institutions include IGOs, INGOs, and international regimes.International institutions produce four positive
results in obtaining international security (Morgan, 2013: 32-34).

The Constructivist approach, formed by imported ideas from sociology on construction of national identities, has put a deep influence in the analyses of security in international politics after the end of the Cold War. On the other hand, Identity is of key importance for the Constructivist view because it defines who the actor is and what its interests and preferences are. 

There are criticisms directed towards the Securitisation approach on various grounds.

First,  the Securitisation presents a strong subjectivist knowledge because it is exclusively a ‘speech act’ not having a direct correspondence to realities of external world (Dannreuther, 2007: 43). 

Second, there is always a blur distinction between the boundaries of political and security realms. The Securitisation approach inclines to set the security apart as a value, and divide the domains of politics and security (Ibid).

Third, closely linked to blurred distinction between securitisation and politicisa-tion, the process of securitisation can be abused to legitimise and empower      certain bureaucratic or civilian groups in power in a country.

Fourth, the Securitisation is a Eurocentric approach reflecting much of the concerns of postmodern implications of European integration process.

He means to put forward the idea that spread of nuclear weapons would repeat the stability experienced in the example of the relationship between the US
and the USSR.

Similar to economic interdependence model, empirical data suggest that democratic peace argument is largely relevant to the relationships in the North, particularly in the relationship within the EU and between the US and Europe.

The nuclear balance has provided a relative peace and security between great powers. Economic benefits of peace is also of great value in the post-Cold War era. The Cold War came to an end between the US and the USSR with the domestic political and economic reform policy of the latter in order to resemble the former.

Economic interdependence is one of the basic arguments of the Liberal school of thought. States having adopted free trade and worked for economic integration, are in a position of win-win with the states they interact in an interdependent
manner.

France did not even trust the security guaranties of the US and NATO. It left NATO’s integrated military command structure in 1966, and developed and stockpiled its own nuclear arsenal independently in the years between 1960 and 1996.

The US and China as the biggest economic powers in the world are economically interdependent since both states are second and first trading partners of one another.

Similar to economic interdependence model, empirical data suggest that democratic peace argument is largely relevant to the relationships in the North, particularly in the relationship within the EU and between the US and Europe.

Waltz argues that the more nuclear weapons the better. He means to put forward the idea that spread of nuclear weapons would repeat the stability experienced in the example of the relationship between the US and the USSR.

Widespread poverty in the South are caused by various negative factors such as environmental degradation, lack of clean water, absence of enough energy, and so on.

Security is a prerequisite for development, but development does not always provide security for many cases in the South and the North. Development brings about prosperity, stability, and cohesion, but it also creates inequality, social stratification, and individual and group estrangement.

Many people and political figures in the developing world have increasingly seen the developed North as a barrier, exclusive body, and discriminatory in the latter’s efforts to stop the flow of people escaping from poverty, violence, and prosecution.