As our societies have grown larger, and communications have become global and fast-paced, our bodies and minds have been subjected to a mental stress different from the "fight or flight" situations we have adapted to through evolution. Furthermore, mental health issues are now seen to be on the rise all over the world. Globalisation has enabled social crises of different origins, e.g. financial or biological, to influence nations worldwide and spread faster than ever before. This thesis aims to investigate how populations are affected in regard to stress and mental health by the extraordinary circumstances of the global financial crisis of 2008 and the COVID-19 pandemic of 2020-2023.The first two studies in this thesis focus on the effects of the financial crisis on young adults (Paper I) and adults in working ages (Paper II). Greece was severely affected by the global financial crisis of 2008 and went into a decade long recession, whereas Scandinavian countries were less affected. University students were recruited from the psychology and medicine programs in Athens, Greece and Linköping, Sweden. Primary care visitors were recruited consecutively at primary health care centres (PHCC) in Greece, Sweden, and Norway. Data was collected in connection to recruitment. All participants filled out the same short questionnaire and gave hair samples that were analysed for cortisol concentrations (HCC) as a biological measure of stress.