Edo Tensei, or Impure World Reincarnation, is one of the strongest techniques in the World. It was created by Tobirama Senju, and later perfected by both Orochimaru and Kabuto Yakushi. Edo Tensei gives they user an arsenal of undying Zombies. But there are a few ways to counter it.
Probably the simplest of all known ways to counter Edo Tensei is sealing Jutsu. The reincarnations cannot die. They keep on regenerating from any damage they take. So, naturally the best way to defeat them is by sealing them. The Allied Shinobi Forces also utilized a special sealing squad to do the job, which consisted of several strong Shinobi like Sai, Kankuro, Mai, etc.