Known to humanity as The Pattern, it was discovered ten years before the Second Battle of Sol, and shook humanity to the core.
The truth of it is simple, that the Shiplords do not take one price, but many. They leave a race to rebuild, to grow anew, and then when they can be sure that there will be enough to merit the trip they return and seek to strip a world anew. The Tribute Cycle is one seemingly engineered to force a race to attempt to break out from it, those who break or fail to put up sufficient resistance being wiped out by the Tribute Fleets. If a Tributary violates the Directives, they are also wiped out, though in some cases this has involved the deployment of Regular or even War Fleet forces.