Minecraft – Why is villager breeding failing in a village

You will need to return at least 2 villagers. Then they will start repopulating the village. As of 1.2, villagers will mate and repopulate based on the number of available houses. See this post (especially the "your village died out" section) for more information.

As of the 1.8 snapshots, though, the villagers need to be "willing" to breed in order to breed. It seems that you can make a villager "willing" by trading with them. Willingness is granted on the first new trade offer, and at a 1 in 5 chance per subsequent trade. Once a villager is willing, they will immediately seek another willing mate, if the village can sustain more villagers (based on the number of houses).

Villagers have reputation as well as willingness. -30 is the minimum while 30 is the maximum reputation. They will stop breeding when you lose reputation.

Here is some info on reputation.

http://minecraft.wikia.com/wiki/Reputation

I have also read 5 or 3 minute cool down after a pair breed for those two that did breed. Untested though!