What does break the floodgates of countless uncried tears mean

A floodgate is what it sounds like - a gate that holds back dangerous waters from something that needs to be protected; typically some sort of shoreline civilization.  To break it sets the water forth, which is represented as tears here.  This basically means that whatever was stopping that character from crying, whether it be pride, the situation, or other factors, is now gone, and they're ready to let out all of their pent-up tears.

his humanity shines from every page as he bears witness to the tragedy which befell the jewish race at the hands of the nazis. wiesel was a romanian-born jew whose home town of sighet was occupied by the hungarians for most of the second world war. in may 1944, all the jews in the area were forced into cattle wagons and transported to auschwitz.

animal farm, written by george orwell, is a representation of russia after the revolution that led stalin to take over power.

in this excerpt, the central idea seems to be that the animals (a representation of society), when they believe to be working for a greater good and equality, are obedient and productive. they were convinced that, after expelling the owner (jones) from the farm, they would live in harmony and be fairly treated.

as we know, the pigs become the leaders and grow more selfish and dictatorial with time. in the end, they look and act in a way so similar to humans that it is impossible to tell the difference. the ideals of equality are shattered, and the farm turns out to be worse than it was before. the animals are manipulated with false propaganda and forced to work in order to enrich the pigs.