The most severe punishment one group of countries has placed upon another.
France especially levied heavy reparations on Germany. This resulted in the ruining of the German economy, causing starvation and raising social and political unrest.
It is interesting that France actually started WW1. Austria Hungary was totally within it's rights as a sovereign Nation to act upon the uprising in Serbia. Deciding to declare war brought the world close to it's knees.
It's not surprising that the terms of the treaty of Versailles brought rise to National Socialism and Hitler through a populous movement.
In final analysis, the Treaty of Versailles was in essence a treaty designed to start WW2.