Episode:Rising, Part 2

The Wraith have captured many of the Athosians and Atlantis expedition members, before leaving through the Stargate. When Major Sheppard comes back with refugies to the newly found city of Atlantis, he discovers that the city is on the verge to collapse.

Answered questions

 * Why did the Wraith come for culling just few moments after the Atlantis expedition arrival on Athos?