The Beckoning is a phenomenon amongst Kindred of Generations Ninth or lower, wherein they are compelled to travel to the general area of the Middle East and other regions that supported early human civilization, especially the Levant and the Maghreb. This effect seemingly began around the same time as the Sabbat's Gehenna Crusade, and the few Elders that do avoid it tend to hole themselves in their domains, feasting off of the blood of Neonates.
The precise nature and origin of the Beckoning is unclear, though the Antediluvians are of course highly suspect as its source; as are the Methuselah of the region. An extreme psychological event, such as the breaking of an old blood bond, may be able to temporarily stave off the effect of the Beckoning, as may diablerie or consuming potent Kindred vitae. The truth is unclear, and many hearing its siren call scramble in an effort to resist.
It is a little known fact that the Elders of Clan Hecata are not affected by the Beckoning, perhaps already having built a resistance after Cappadocius' "beckoning" of the original Clan of Death to the Feast of Folly. There are many other internal theories, including the idea that the formation of the Hecata itself is a kind of Beckoning. No other group of vampires shares this resistance; even Caitiff of suitably potent Blood feel the call.
The scope of the Beckoning and the Gehenna War were originally limited to the Middle East, as shown by the Corebook, and early versions of Camarilla, which were changed to make it a more widespread event across Europe as well. In Sabbat: The Black Hand however, it is clarified that it is a global event.