The revelations are stunning for what had been respected institutions. How did the Swedes and Danes get sucked into underworld relationships? Why are American investigators — federal and New York State — poring over their accounts? And how does this all harken back to the fall of Communism two decades ago?

Here are the answers to those and other questions.

For a Danish bank, trouble in Estonia

Danske Bank has admitted that its Estonian subsidiary helped thousands of customers, most of whom were not residents of Estonia, to launder tens of billions of euros from 2007 to 2015.

Over the years, Danske Bank managers ignored or played down warnings about suspicious transactions by Estonian regulators, the Russian central bank, partner banks and its own internal auditors. The Estonian operation processed transactions worth 200 billion euros, or $225 billion, involving foreigners and generated profits far out of proportion to its size. The Danish bank regulator took little action and its money laundering unit was woefully understaffed.

Danske Bank did not acknowledge the problems until 2017, after Danish media reported on them. The full scale of the wrongdoing did not become publicly known until September 2018, when Danske Bank released an investigation conducted by an outside law firm. The bank admitted that it had “clearly failed to live up to its responsibility” and the chief executive, Thomas Borgen, resigned under pressure.

How did Sweden come under scrutiny?

The allegations against Swedbank, which also involve its operations in the Baltics, have come to light in recent months after reports by Swedish public television. But the New York Department of Financial Services had been looking into possible money laundering at Swedbank for at least a year.