The case for a pernicious persistent current account deficit is easy to build: the home country is borrowing abroad for a long period and that debt may reach a point of becoming unsustainable. There are several ways to put pressure of the debtor to ensure repayment. The home private and government agents may self-regulate their spending, by incorporating their future expectations of what happens when their debt is no longer repayable (not likely). Another way is by market forces, if creditors think the home country is no longer able to service its debt, then funds for home will disappear, or there could be political pressure for repayment.
However, for Balance of trade surpluses, there doesn't seem to exist any 'economic' force at work for a downward pressure... or is it?
For example Germany has been amassing enormous surpluses since the 70's, and recently, their surpluses have reach 8.5% of GDP in 2015. How does one explain this 'economically'?
Any help would be appreciated.