Why have some Western liberal democracies experienced more right-wing terrorism and violence (RTV) than others? This question remains largely unanswered in existing research on the extreme right because (1) events data suitable for cross-national comparisons have been lacking, and (2) existing analyses fail to capture RTV's causal complexity, which involve multiple causal paths (equifinality) comprising causal conditions that become sufficient for the outcome only in combination (conjunctural causation). To help fill these gaps, this paper uses new events data from the RTV dataset in a qualitative comparative analysis (QCA) research design, aiming to explain variation in the extent of RTV in 18 West European countries between 1990 and 2015. In doing so, the paper identifies two "causal recipes" that consistently distinguish countries with extensive RTV experience from those with low or moderate RTV experience. The first (North European) recipe involves the combination of high immigration, low electoral support for anti-immigration (radical right) parties, and extensive public repression of radical right actors and opinions. The second (South European) recipe involves the combination of socio-economic hardship, authoritarian legacies, and extensive left-wing terrorism and militancy. Notably, both recipes contain elements of "grievances" and "opportunities", suggesting that these two theories, which are conventionally seen as contrasting, may be more fruitfully seen as complementary. Furthermore, a highly polarized conflict between far right activists and their enemies represents a third necessary condition for extensive RTV to occur. A key to combating violent extremism on the far right therefore lies in disrupting rather than accelerating such polarization mechanisms, suggesting that openness and dialogue might work better than public repression, stigmatization, or aggressive confrontation.