The article looks at how banking crises spread internationally during the 2007-2009 financial crisis. It finds that crises are often caused by both systematic (overall market conditions) and idiosyncratic (specific to a country) factors. When a crisis spreads from another country through idiosyncratic factors, it increases the chance of a crisis in the domestic banking system by 27%. However, exposure through systematic factors doesn't always lead to a crisis. This suggests that reducing idiosyncratic contagion can help lessen the impact of banking crises on the domestic economy.