The Treaty Of Versailles ordered Germany to pay ‘reparations’ to the allies for all the damage they caused during the 1^st World War. The Treaty fixed that amount at 132,000 million Gold Mark, which is about £112,000 million in today’s terms.  

The reparations caused severe stress on the German economy, and after the first enstallement they announced that they could no longer pay.

The reparations also meant that the German economy went into hyper-inflation, making the mark worthless.