Explain the merits of the following statement: Eurocrisis

Explain the merits of the following statement: ” Peripheral EU countries, notably Greece, Portugal, Ireland and Spain, over-borrowed. Simultaneously, peripheral countries experienced exceedingly large current account (CA) deficits. These two phenomena during the 2000-2007 period are key to our understanding of the current Euro-Zone crisis.” Why was the Euro-Zone crisis less severe in Northern countries, which did not over-invest in the non-tradable sector?