Lack of Affection
Most of the times, a pet begins to communicate the need for affection. Like a human being, pets and especially cats are very social animals and need to be cared for like anything else. They deserve to be loved since you have taken the responsibility of raising and keeping them. If the meow is one that brings the cat towards you, it is most likely one that just wants to be loved and cared for even more.
If you have other pets in the house and there is a lot of interaction between them, the cat might be feeling scared and is in the need of protection. Like children playing in a playground, there are those kids that intimidate others, forcing the intimidated to retaliate and go back to their parents. Cats react in the same way. You will need to accompany them when the interaction with other animals is going on so that they know you are supervising their actions.
Hungry or Thirsty
Another very common factor that forces cats to start meowing uncontrollably is hunger or thirst, so make sure that their food container is always full with food and water in order to take that issue away. If the meowing is still consistent after the cat has eaten, it could something else which may just need medical attention.
Your cat may need medical attention if the condition seems to persist after you have tried all previous methods. He/She may also need to be neutered because they begin to meow at night due to being in heat and this may potentially make them more and more aggressive with passing time. Like humans, if there seems to be anything wrong, going to the doctor should be a first option and in this case, a veterinarian.