This paper highlights the overlooked role of prior grievances stemming from historical territorial loss as a significant factor behind support for ethnopopulist parties. While not essential for the emergence of ethnopopulism, territorial loss uniquely aligns with the backward-looking victimization framing crucial to these parties’ electoral success. Utilizing cross-national experimental and observational data from original surveys conducted in 2020–2021 in Romania, Hungary, Germany, and Turkey, we establish territorial loss attitudes as a robust predictor of ethnopopulist party support. In addition to variations in national context, a trade-off emerges for governing populists, revealing that priming past losses attracts concerned voters but alienates those indifferent to territorial issues. Analyzing a quasi-natural experiment involving a new ethnopopulist party that emerged in Romania between waves, we conclude that loss attitudes are stable over time and temporally prior to support for populism.