Why did the Akatsuki capture all the dead bodys and bring it back?

The first and second hokages were sealed with the Death Reaper seal, so they can't be ressurected....

And all of those dead bodies were brought back with Edo Tensei, or the Impure World Reanimation Technique. It's one of Orochimaru's forbiden jutsus.

The way Edo Tensei works is that the summoner or performer of the jutsu has to take some DNA from the dead person, then they have to make a human sacrifice to use it as the dead person's vessel, then they smear a special scroll with the DNA and then, the vessel's old body metamorphosizes into the way the now revived guy's body was at the time a little before they died. They have all their old jutsus and powers as they did in their old lives.

One things is that they may look like them, act like them, and have the same memories as the did before they died, but they aren't really them. Also, the only way to get rid of them is to seal them in some way. No matter how many times you kill it, it will only come back to life.

Anyway, to get to the point, they are going to use them as soldiers in the Fourth Great Ninja War.

They basically made an undead army. Think about it, you don't have to feed them, they don't sleep, they do as they're told and don't ask questions, they don't get tired, and they are some of the best ninja ever! You can't go wrong with an undead army. Oh and they can't die again!

kabuto got all the boodies besides tobi for the edo tensei during the 4th great world shinobi war