Are there any examples from history and/or literature that prove that groups are stronger that individuals?
I think Animal Farm, Lord of the Flies, and The Outsiders are wonderful examples of literature that shows that a team can be stronger by uniting the best of each of the team member's traits to achieve a common goal.
For example, in Animal Farm things began to go sour after the eviction of Snowball from Napoleon's rule. This shows how Snowball was a welcome part of a winning team: Without him, the team is incomplete, and Napoleon could have never ruled so strongly by himself.
In Lord of the Flies the main character has to find strength in people he can trust in order to survive the terrible situation that they are living. The death of Piggy leaves a strong void in the story. Like Snowball, Piggy is also a strong part of a complete set and Ralph would never be the same again.
Therefore, stories like these show us the importance of team work and of social connection for the overall success of our goals.
Interestingly enough, Chaucer's The Canterbury Tales may very well show that the group is stronger than the individual. For one thing, the group chose to travel as a group instead of continuing on their separate ways. One reason they chose so was that there is safety in numbers when encountering dangerous forces, like highway robbers. For another thing, they chose to entertain and enlighten each other through, hopefully, edifying--or at least entertaining--tales as they traveled. The group, then, is greater than the individual because one person's wisdom becomes the wisdom of the group, thus rendering the group stronger than the individual members.
We can't prove this idea because it is not clearly true. However, there are examples that suggest that it is true.
For example, the Civil Rights Movement suggests that this is true. The Civil Rights Movement was strong because of the dedication of thousands of people. There was no way any one person (even a president) could push strong civil rights legislation through Congress. That is why there were weak civil rights bills in the '50s. But then the movement arose and the thousands of people were heard and much stronger civil rights bills were enacted in the '60s.
In literature, William Golding's The Lord of the Flies is a great example of a group being stronger than an individual. The boys on this island are all boarding school students, but they are from different schools and (other than the choir) are connected only by their plane wreck experience. The boys shift their alliances over the course of the story, and most of them are drawn to the savagery of hunting and killing. By the end of the novel, several boys have been killed and every single boy on the island has banded together to hunt and kill the lone remaining boy with a voice of reason. It's not uncommon in either literature or history for this pattern to repeat because it is the pattern of human nature. I'm not sure this example proves that groups are stronger than individuals, but it certainly demonstrates that principle.
I think that history and literature actually point to different answers to that question. History seems to suggest that groups are more powerful than individuals. It usually takes a mass of individuals to effect historical change. Even when kings or dictators issue decrees, it's the group that carries out the decrees. In literature however, it seems that individuals have great influence. At one level that's self-evident; individuals, not groups, write books. But beyond that, I think literature is one of the areas of human enterprise that is still highly individualistic. Franz Kafka pretty much single-handedly transformed the idea of the modern novel. Edgar Allan Poe introduced elements into American poetry that remain to this day. There are important individuals in history as well, but they do not act alone.
It seems like large groups most often create a more powerful alliance than a single individual. The American Revolution and the secession of the Southern states that precipitated the Civil War are two such examples. As popular and powerful as Washington and Lincoln were, it was the power of the people who first created and then decided those two events.
The one that immediately popped into my mind was the 1992 Los Angeles Riots.
As you may recall, after several police officers were acquitted of assaulting Rodney King, the city exploded in protests, looting, and violence.
One of the most disturbing moments during that time, which speaks to the power of "mob mentality" is when a lone truck driver (Reginald Denny) happened to stop at a stop light in the middle of all the frenzy. A group of young men dragged him from his vehicle, and together assaulted him near to death. Denny was powerless (both rationally and physically) against the group who had decided that he was somehow connected to the incident.
The first example I thought of was the French Revolution, where large groups of the French public rose up against the individuals in the ruling class of the monarchy. They proceeded to kill thousands of aristocrats as their group-rage mentality led to a bloodbath in the streets of Paris.
Another example might be other revolutions or one could examine instances where a movement seemed to be embodied in one individual but the movement continued to gain strength after that individual's death. Martin Luther King Jr.'s death certainly dealt a blow to the civil rights movement in the United States but of course because large groups of people continued to agitate and vote for change, that change continued to happen even after the death of a very powerful and important individual within that movement.