The Northwest Iberian Peninsula is not a uniform region. Geographers have divided it into two main biogeographic sub-regions: Atlantic and Mediterranean, each with its own characteristics, in terms of geomorphology and climate. The perception that these two sub-regions have distinct identities since, at least, the first half of the 3rd millennium BCE, i.e. since the Chalcolithic period, has led us to analyse separately developments in the last quarter of the 3rd millennium BCE, which is viewed as a key period for understanding the emergence of the Bronze Age.During the Early Bronze Age new settlement strategies emerged in the Atlantic sub-region, associated with the appearance of innovative pottery shapes and decorations, resettlement of high-altitude areas for burial in small cairns, circulation of new prestigious metallic icons, the emergence of new styles of rock art, such as engravings of dozens of halberds, the emergence of the phenomenon of structured depositions of metallic objects, such as the deposits of halberds, or halberds and daggers, and, consequently, new social relationships, new power structures and new places for negotiating social relations, which revealed significant structural changes compared to Chalcolithic communities.In the Mediterranean sub-region, despite new locations for certain settlements, changes seem to have occurred across a broader timeframe, including the abandonment of several community and ceremonial spaces -such as walled enclosures or shelters with collective depositions -, the emergence of metallic deposits, consisting of halberds, and the timid adoption of new iconographies in rock art. These are characterised by phenomena of continuity or social resistance, and reveal that, in this region, social changes and new scenarios of power or social aggregation occurred in a manner that differed from the Atlantic sub-region.On the basis of the analysed data it seems possible to hypothesise that, during the last quarter of the 3rd millennium BCE, together with the phenomena of social resistance and permeability to new developments, the Northwest Iberian Peninsula was subjected to multiple and distinct influences that spawned the development of a mosaic of societies, apparently united and standardised by generalised phenomena.The factors that contributed to this change were multiple and distinct in each of the two sub-regions. This includes important external factors, such as the climate conditions in the middle of the 3rd millennium BCE and events that occurred during the second half of this millennium, that had distinct repercussions on the two sub-regions; greater or lesser permeability to Atlantic contacts; 'dismantling' of supra-regional exchange networks with southern regions, as a result of social upheavals in the Southern Mediterranean. In terms of internal factors, it is worth highlighting the capacity for resilience and adaptation to changes. Phenomena such as the migration of populations of Pontic-Caspian origin during the second half of the 3rd millennium BCE, revealed ...