Defence matters do not exist in a vacuum: they are always influenced by the actual political environment, the current political milieu. This is the case with defence collaborations in Europe as well. Without a supportive political milieu, those defence policy communities (DPCs) that want to cooperate with each other would be working in a void with no outside support, which would make their efforts to launch a multinational defence cooperation (MDC) very difficult or even impossible. A supportive political milieu helps to galvanize wider support for the MDC and can help to mobilize proponents from outside the enthusiastic members of the cooperating DPCs too. This may provide ‘firepower’ for the advocates of a new MDC to convince and change the attitudes of those who are sceptical or even hostile to the idea inside and outside the DPC. Thus a supportive political milieu for the creation of a new subregional MDC is a situational factor that is often necessary for a new defence collaboration to be initiated.

In general, the attitudes of actors regarding political issues ‘are powerfully conditioned by the social and political milieu in which they take place’ (Weatherford, 1982). For instance examining how political attitudes changed during the 1980 presidential campaign in the US, Michael MacKuen and Courtney Brown found that ‘the impact of an individual’s milieu on attitude change is greater than the effect of a respondent’s sex, age, or education […] the respondent’s race, information level, income, and ideology’ (MacKuen and Brown, 1987: 477). They also demonstrate that, although the political milieu of the macroenvironment is relevant in this regard, the content of the discussion in the microenvironment of the studied individuals has an even bigger impact on their political attitude. This affects communities differently, creating an unstable and dynamic nature for the contemporary political context (MacKuen and Brown, 1987: 485).

Building on the insights of MacKuen and Brown, this book understands the political milieu on two levels: the microenvironment and the macroenvironment. The microenvironment is where the discussions and the policy formulation happen inside a DPC (Roberts, 2020) and between relevant DPCs. However, this conversation is influenced by the events and processes of the macroenvironment.