Black Lives Matter (BLM) has gained momentum in its fight against racism cross-nationally. Yet, there are conflicting opinions on BLM. To account for this, previous research relied on cross-national predictors (e.g., Social Dominance Orientation; SDO). However, BLM support needs to be examined via the prism of national contexts and their peculiarities. Here, we claim that nationally-grounded determinants (next to cross-national ones) shape BLM (dis-)approval. Based on national identity construal, we argue that the way individuals identify with it predicts BLM support. Further, we expect this relationship to be mediated by personal endorsement of national beliefs about diversity. This claim was tested in a French ecological context, where: 1) national identity is based on a straitened view of diversity and 2) diversity issues are regulated via two antagonistic cultural norms: one is egalitarian (i.e., Historic La&iuml;cit&eacute;) and the other is assimilationist (i.e., New La&iuml;cit&eacute;). In two pre-registered and well-powered studies (Study 1, N = 305; Study 2, N = 489), we anticipated and found that National Identification negatively predicts BLM support. Crucially, cultural norm endorsements dually-mediated this relationship, suggesting their instrumental function in BLM support. We considered, via path analysis, an additional pathway involving SDO. We found that nationally-grounded and cross-national paths operate jointly to shape BLM support. We replicated these results one year later, providing support for our model. These findings are of relevance beyond the French context as they contribute to an emerging literature examining how intra- and inter-national forces shape, in tandem, diversity responses.< Réduire