'All power flows from the barrel of a gun'. Discuss.

This sort of question appears nebulous at first glance, however, it can be answered both methodically and in an interesting manner, while touching on a variety of political ideologies and concepts. The topic of the question is evident from the key word upon which it is centred (i.e. 'power'), and therefore invites a discussion on the nature of power. The section of the quotation above that states 'flows from the barrel of a gun' refers to coercion, and so, to simplify the quotation, it is essentially stating that all forms of power flow from coercion. There are political theorists such as Weber, who would argue that the power of the state originates from its monopoly on the ability to coerce its subjects. And indeed, a practical analysis of Stalinist Russia and Mao's China would suggest that coercion was a key factor that establishes a leader's power. So, there is an element of truth in the statement.
Once a strong case has been made for the idea that power is rooted in coercion, it is important to consider alternative perspectives and contrast the strengths and weaknesses of these positions with the position advanced in the quotation. To do so, one would consider that Lukes, for instance, argues that there are actually three faces of power, (1) decision-making, (2) non decision-making, and (3) ideological power. Lukes' conception of power is therefore fundamentally different from that of a Hobbesian or Weberian conception of coercive power. In addition Bachrach and Baratz consider that power may exist in the form of agenda setting. This is demonstrated, for example, by the 2016 EU membership referendum. Even though parties such as UKIP did not possess decision-making power, they placed issues such as immigration and parliamentary sovereignty in the public eye, which then set the agenda for future political discussion. Likewise, by controlling what does not appear on the agenda for public discourse, political power is exercised. Furthermore, there are also more subtle theories of power, such as the idea that power originates from indoctrination that gives rise to hegemonic beliefs. Notable thinkers from this school of thought include Antonio Gramsci. And, this method of exercising power is not at all based on coercion. For example socialist realism during Stalin's Russia used art and poetry to develop certain ways of thinking, and likewise, it is argued by thinkers such as Chomsky that Marshall Aid during the Cold War was given to European countries by the US to establish hegemonic liberal ideals.
An in depth discussion of both power as coercion and power as all of the alternatives mentioned above, along with careful comparison between the ideas is the key to answering the question above successfully.