Pandemics causing death are linked with increases in support for radical political movements, all the way back to the 1918 flu pandemic and the birth of 20th century fascism
Evidence linking past experiences of worsening health with support for radical political views has generated concerns about the consequences of the COVID-19 pandemic. The influenza pandemic that began in 1918 had a devastating health impact: 4.1 million ...
It looks like me like they just mean that their source for region by region how many people had died, and what the support was for fascism in the elections, was pulling the data from this one specific newspaper at the time.