Greetings,
Insurance companies base the premiums they charge on the level of risk posed by applicants.
In order to measure risk, insurers make use of numerous statistics and reports - including statistics based on nationalities. If statistics show that people which hold a certain citizenship tend to make more claims or be involved in more incidents than people of other nationalities, those statistics may influence the premiums charged.
This system is used within countries as well. For example, in Switzerland people who reside in regions in which a high number of health insurance claims are reported will pay higher health insurance premiums.
Other factors which can influence insurance premiums can include age, gender, habits, insurance claims history, driving history, driving experience and many more.
Best regards from Moneyguru
More on this topic:
Swiss car insurance comparison