In 2006, then Mexican President Felipe Calderón declared a 'war' against criminal organisations that were beginning to control some of the country's territories. Consequently, the number of murders and disappearances of people began to increase steadily by tens of thousands. Far from acknowledging the errors of the strategy, the authorities constantly criminalised the victims and denied the tragic consequences of the use of the military against drug cartels. After the murder of his son on 28 March 2011, the poet Javier Sicilia started leading mobilisations in the state of Morelos to protest the violence. In just a few days, the actions expanded to virtually all regions of the country embracing relatives of victims, activists and organisations of very different backgrounds, forming the Movement for Peace with Justice and Dignity (MPJD). This thesis comprises an in-depth case study of the MPJD. After providing an overview of the context in which the mobilisations started and my research methods, I develop thematic chapters. In the first one, I analyse the recruitment dynamics of the MPJD. These pages contribute to the literature by advancing the understanding of how people without prior political experience or links to a mobilised group join and participate in protest. This, moreover, helps in refining rather than reifying the function of social networks. The second chapter explains the upward scale-shift process of mobilisation and the response given by the government through the analysis of coalition building, framing and counter-framing. The results of the analysis help to specify the conditions that facilitate not only the development of alliances, but also those that lead to their accelerated breakdown. Regarding framing, the work contributes to understanding which attributes facilitate resonance and alignment amongst audiences with contrasting characteristics. Furthermore, the discussion around counter-framing highlights how official responses influence the discursive processes of contentious actors, whose opportunities are not the same in 'the streets' and in official spaces. Next, the third chapter examines the type of social ties formed through the involvement in the contentious performances led by the relatives of victims of extreme violence. Bringing together the literature on social movements and a body of Latin American research on "emotional communities", I argue that the MPJD fostered a political-emotional community in which the public narration of suffering made victims and non-victims coalesce to demand justice collectively. Overall, this chapter advances our understanding of the dynamics through which allies that are not directly aggrieved by extreme violence develop a sense of community with the victims. Likewise, it develops four empirical dimensions for the analysis of political-emotional communities: the role of testimonios (testimonial narratives), the ethics developed during contention, the fluctuations in participation, and the costs and risks involved in the mobilisations. The last two chapters focus on the outcomes of the MPJD. The fourth one encompasses the political and cultural outcomes contributing to the literature in two ways: First, by discussing how achievements in the policy process can demobilise some groups but mobilise others; and second, by explaining how the spillover of a contentious actor can consolidate a social movement community in an emergent contentious field. Finally, the fifth chapter analyses the biographical consequences of participation in victim-led mobilisations. These pages provide an account of how the lives of the participants have been influenced due to their involvement in contention. This chapter advances the understanding of the interplay between social relations and cognitions that lead participants to modify their worldviews. In an academic sense, this thesis introduces a series of thematic chapters that provide empirical evidence to refine several areas of the theory to better understand various processes related to social mobilisation. Regarding the importance that this thesis can have for the activists and the families of the victims, my work is, first, a systematisation of their campaigns and experiences; second, an acknowledgement of the transcendence of the actions that they have been carrying out sustainedly during a decade; and third, this research is a space for memory, so that their names and those of their relatives are not forgotten, so that the demand for justice does not end.