Catalonian secessionism acquired prominence from 2010 onwards. During the last decade secessionist parties won three regional elections and sustained Governments by tiny majorities at the Autonomous Parliament. Two illegal consultations about selfdetermination were called and around 2 million (38% of population census) supported secession from Spain. An "Independence Declaration" was proclaimed on 27th Oct. 2017, followed by suspension of Home Rule sanctioned by Spanish Parliament that endured till mid-2018. The main consequence of the secessionist push was the build-up of a confrontation between two large segments of Catalan citizenry, unionists and secessionists, which was absent before. This study aims to shed light on the rise of secessionism and the appearance of a deep fissure between these communities. By building upon the complete series of data from iterated official polls (88.538 respondents, 45 surveys), the paper displays the evolving changes along the period 2006-2019 of national identity feelings ("sense of belonging"). Along that period, there were increases exceeding 15 percentage points of "only Catalan" national identity and analogous decreases of "equally Catalan and Spanish" dual national identity. The findings disclosed highly significant covariations between changing trends on national identity feelings with: (1) family/mother language, Catalan vs. Spanish; (2) following regional media versus other media. Since language/ascendancy origins and media consumption trends are closely interrelated, within Catalonia, our discussion focuses on the role played by such ethno-cultural cleavage. Further, statistical analysis for longitudinal data identified several turning points linked to singular political events that likely accentuated polarization around the issue of secession. The findings unveil evolving tracks that could help in the understanding of a process that, in a very short time, produced a severe social division within a fully open and democratic society at the heart of Europe.