the green fields of England, while the hoof and horn signified the future Republic of the Animals which would arise when the human race had been finally overthrown."

Flags are ubiquitously deemed to be symbols of patriotism, loyalty, trust and respect, not only for the government or state which it represents, but for any society, organisation or group, no matter how large or small.

The flag represents the unique attributes of whichever order it represents and is a symbol of its history, ethos, fundamental principles and beliefs as well as its mission. As such, it carries with it huge symbolic significance and is, or should, therefore be treated with the utmost respect. Dishonouring a flag is equal to dishonouring who and what it represents. It is for this reason that flags are generally used during formal and ceremonial occasions.

Initially, the flag in Animal Farm represents the ideals of the animals as a collective: freedom from human domination, to fend for themselves (independence) and a general brotherhood (comradeship). The design of the flag closely resembles the flag adopted by the Communists after the Russian Revolution.

The hoof and horn are very similar to the hammer and sickle reflected on the communist flag. The most obvious difference is in the general colour of the flag. The Communist flag had a red background. The hammer and sickle represented the unification of agriculture and industry, whilst the red colour represented revolution.

it is ironic that the flag in Animal Farm represents green fields, which could signify peace and tranquillity, lives of relative comfort and hours of relaxation, as well as freedom from abuse. In reality, the animals were later exposed to the same type of totalitarian control that Mr Jones and his men exercised, when the pigs became more powerful and abused their leadership. Also, the flag later comes to represent this absolute control and becomes a tool for propaganda by the pigs. Attending meetings and performing ritualistic tasks and having compulsory assemblies actually disempowered the animals and they willingly bent to the pigs' will.

Further irony lies in the fact that the hoof and horn symbolise the "future republicof the animals when the humans have been overthrown". This is never to be, for in the end, the pigs come to represent the animals greatest enemy, so much so that:

"The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which."

The flag was made from "an old green tablecloth of Mrs Jones's" upon which Snowball " had painted on it a hoof and a horn in white."

That sounds kind of generic, until you start to visualize it. Then the images fit together to become something very close to the hammer and sickle of the Soviet Union. Creating the flag was a sign that the animals had become ever more like what they hated (the ruling class, the humans, etc.). Historically, the flag symbolizes the Soviet betrayal of the workers, and the distortion of their ideals.

George Orwell certainly did put in a great deal of work to fill his novel Animal Farm with symbolism to illustrate his themes. We can see symbolic reasons behind his animal choices.
Orwell uses pigs to symbolize the leaders of what was actually the Bolshevik Revolution and the start of communism in Russia because pigs are actually known to be the most intelligent animals found on a farm, next to dogs. Studies have shown that pigs are able to use mirrors to their advantage and do all kinds of tricks, including "jump hoops, bow and stand, spin and make wordlike sounds on command, roll out rugs, herd sheep, close and open cages, play videogames with joysticks, and more" (Angier, "Pigs Prove to be Smart, if Not Vain"). Hence, it was most definitely appropriate for Orwell to symbolize Carl Marx, leader of Russia's communist revolution, as an old, wise pig named Old Major. What's more, pigs are also known to represent uncleanliness as can be seen in the fact that they are known to wallow in mud and eat any slop and in the fact that pigs are forbidden cuisine in many religions like Judaism. Uncleanliness can also be likened to moral depravity; hence, it's also very fitting for Orwell to use the pig Napoleon to symbolize Stalin, the pig Snowball to symbolize Trotsky, and other pigs to represent other aspects of Stalin's regime.
Boxer is a horse whose motto is always "I will work harder." Boxer symbolizes the Russian people in general. Horses are known for their loyalty and their willingness to work, making horses a perfect way to symbolize the willing people of Russia.
Benjamin is a donkey who always questions the rightness of the pigs and refuses to do as they say because he sees any action as being futile; no matter what anyone does, "hunger, hardship, and disappointment" will always be, as he says, "the unalterable law of life" (Ch. X). What's more, Benjamin remembers every detail of the farm's difficult life. Benjamin symbolizes the older, cynical Russian citizens who did not believe communism would benefit society and even saw communism's evil side. Using a donkey is a perfect way to symbolize cynical citizens because donkeys are known to be stubborn, have good memories, and are unwilling to do anything that's not safe (Mike's Donkeys, "Donkey Facts").

The idea of using animals in a satiric allegory has a long history. Probably the most famous example, prior to Animal Farm, is in Book IV of Swift's Gulliver's Travels, in which Gulliver encounters the realm of the Houyhnhnms, a race of intelligent horses who embody virtues that human beings, in Swift's view, lack. In John Dryden's satiric religious allegory The Hind and the Panther, the two title animals represent, respectively, the Roman Catholic Church and the Church of England. But your question as to why Orwell uses animals in his own satirical work can best be answered if you look first at the actual events of human history portrayed by Orwell in allegorical terms.

If we see Animal Farm in its most specific meaning as a parable about the Russian Revolution, the animals symbolize the Russian people apart from the ruling class of the Czar and his administration, the aristocracy, and the wealthy people generally. In less specific terms, the animals can be seen to stand for working-class people or, more broadly, non-wealthy people in any place and time throughout history. The wealthy, the rulers, are symbolized by the human Mr. Jones, the owner of the Manor Farm before the animals chase him out. Orwell is making the sharpest contrast possible in his portrayal of the ruling class, on the one hand, and the rest of the population—especially the working class—on the other. By making it a human vs. animal distinction, any doubts should be erased about how severely working people, in Orwell's view, have been oppressed throughout history.

But as in other satires, the use of animals also gives an irreverent, humorous tone to the allegory, in spite of Orwell's sympathies obviously being so strongly with the ordinary working people of the world. This is in keeping with the rather cynical message of his fable, in which it turns out that even among the oppressed ones who carry out the Revolution there are those who are primarily interested in seizing power for themselves, rather than in helping the other "animals."

This, of course, is exactly what happened in the actual history of the Soviet Union. What presumably was meant to be a workers' state with equality for all ended up a brutal dictatorship under Stalin, who made Russia even less free than it had been under the czars and killed millions of his own people.

To understand why Orwell wrote Animal Farm as an allegory, it is useful to look at his explanation in the Preface to the Ukrainian Edition in which he outlines two key reasons.

Firstly, Orwell states that he felt compelled to tell the world about the horrors being committed by Stalin in the USSR:

"It was of the utmost importance to me that people in western Europe should see the Soviet regime for what it really was."

For Orwell, Stalin's politics were so far removed from true Socialism that he wanted to tell the world about it.

Secondly, he wanted to portray this story in a way which made it easy for people to understand:

"I thought of exposing the Soviet myth in a story that could be easily understood by almost anyone and which could be easily translated into other languages."

The inspiration for a farmyard came a short time later when he saw a little boy, aged around ten years old, driving a "huge cart-horse" and whipping it "whenever he tried to turn." It suddenly occurred to Orwell that if this animal realised its strength, it could easily overpower the boy and the rest of our society. From this, Animal Farm was born. 

To read the Preface in full, please see the first reference link provided.

On one level, Orwell wanted to write a fable that could be enjoyed by people of all ages and situations. By using animals as characters for the story, he was following the pattern of many previous writers of fables, dating all the way back to Aesop. Other characteristics of the story also follow the traditional format used in telling fables.

On a deeper level, Orwell wanted to express his condemnation of the rise to power of the Soviets and the evils he saw in the leadership of the Communist Party. The book was written during World War II, at which time England was an ally of the Soviet Union against Germany, so a book condemning the Soviet Union was a politically unpopular thing to write. The book was not published until after the War in Europe had been concluded.

In an allegory, characters and events stand for something else. In this case, the characters in the novel stand for significant figures in twentieth-century Russian history.

By presenting his story as an allegory, Orwell was able to highlight actions, attitudes, and characteristics of the historic figures he was portraying without directly identifying any of those people. He presented the story and allowed the readers to draw their own conclusions and find their own lessons - the ultimate purpose of an allegorical story.

The animals have staged an uprising and driven Mr. Jones and his wife from the farm. The Animalist revolution has triumphed, and a new farm—Animal Farm—has established to serve the interests of the animals themselves. In the first flush of their revolutionary ardor, the animals decide that the new farm requires its own flag, a symbol of the momentous changes that have just taken place.

They find what they're looking for when Snowball discovers an old green tablecloth in the harness-room. He takes the tablecloth and paints a white hoof and a horn on it. As Snowball explains, the green represents the fields of England, while the horn and the hoof signify the future Republic of the Animal, which will be established when the hated human race is finally overthrown. The flag is run up the flagpole in the farmhouse garden every Sunday morning, a visible symbol of the revolution's success and what it stands for.

The allegorical satire of Animal Farm is amplified by the use of talking animals  There is a dark moral in Animal Farm,but it is accepted because it is presented in a humorous, nonthreatening way.

The idea that animals could work together cooperatively to overthrow their human bondage is laughable and really ludicrous if you think about it deeply.  So, what perfect way to show the inequality of class in society than by showing how the pigs eventually took over the idylic farm and became totalitarian rulers exactly like the humans had done.

By using animals, Orwell was able to avoid the psychological implications that would have come up had he used human beings as characters.  He is able to use the pigs to degrade the Russian Communist leaders, the sheep as the masses, the horse as the steady plodding worker who carries more than his fair share of the burdens. People who were accustomed to farm animals and their roles in farm life would have been able to relate to the attributes that Orwell gave to these animals.

There could be a number of reasons for this.  One that comes to mind is that the story has a lot of qualities of the fable which usually uses animals with human qualities to make a point.  (Consider Aesop's Fables such as "The Hare and the Tortoise" and "The Fox and the Grapes").

Another reason might be to make those he was targeting appear foolish.  What nicer way to do this than call the leaders "pigs"?  Sheep represent the masses that are easily led astray and these could be seen as an allusion to some of Jesus's New Testament teachings.  Also, making the characters animals makes it easier to not have to define human features that may mislead the reader into thinking of an unintended target for the satire.

In Animal Farm, Orwell uses a number of symbols to draw the reader's attention to the inequalities which plague the farm and to reinforce some of his key themes. 

Sugarcandy Mountain, for example, is an important symbol in the book which first appears in Chapter Two. It is described as "animal heaven;" an afterlife in which animals never work and can eat sugar lumps which grow on the hedges (see reference link). By positioning this symbol at the beginning of Chapter Two, before the revolution takes place, Orwell uses Sugarcandy Mountain as a sort of "utopia" for the animals in which they can dream of a better life beyond the tyranny of Mr Jones (see reference link). It is interesting to note that Sugarcandy Mountain also appears in Chapter Nine of the novel, just after Napoleon is proclaimed the President of Animal Farm. In this respect, Orwell uses Sugarcandy Mountain to represent the desperation and misery of the animals under Napoleon and to make the important point that their lives are no better than they had been under Mr Jones. To put it bluntly, the revolution has failed to live up to its expectations. As the narrator comments: 

Their lives now, they reasoned were hungry and laborious; was it not right and just that a better world should exist somewhere else?

Similarly, Orwell uses the barn to symbolise the hopes and dreams of these repressed animals. In Chapter Two, for instance, the barn is used as a canvas for the Seven Commandments, in which all animals are proclaimed equal and humans are identified as the enemy. The barn is also the setting for Old Major's speech (in Chapter One) which inspires the animals to revolt in the first place. But Orwell also uses the barn to demonstrate how the hopes and dreams of the animals are crushed by the supremacy of the pigs. This begins when the pigs move out the barn, in Chapter Six, and begin sleeping in the farmhouse (another symbol of inequality). Later, in the final chapter, the animals read Napoleon's amended commandments on the wall of the barn. Here, they learn the extent of Napoleon's brutal dictatorship: that all animals are equal but some are more equal than others. 

In the tradition of such great satirists as Voltaire and Swift, George Orwell has written an allegory as the medium of his pointed criticism of Soviet Russia and Communism.  The animals used as characters represent various people and types; by using these animals, Orwell depicts concepts in an easily identifiable way. As explanation, Orwell himself wrote that he attempted in his novel "to fuse political purpose and artistic purpose into one whole."

In the preface to his novella, Animal Farm, Orwell, who was a socialist, describes how the idea of setting the book on a farm came to him:

...I saw a little boy, perhaps ten years old, driving a huge carthorse along a narrow path, whipping it whenever it tried to turn. It struck me that if only such animals became aware of their strength we should have no power over them, and that men exploit animals in much the same way as the rich exploit the proletariat.

"Snowball was in league with Jones from the very start!  He was Jones's secret agent all the time....Did we not see for ourselves how he attempted--fortunately without success--to et us defeated and destroyed at the Battle of the Cowshed?"

George Orwell wrote his allegory titled Animal Farm, a satire on the Soviet Union and its dictator, Joseph Stalin, during the middle of World War II.  Before the war, Stalin and the Soviets had been the ideological enemies of Adolf Hitler and Nazi Germany.  Just before the war broke out, Stalin found it convenient to sign a non-aggression pact with Hitler – a move that shocked and disillusioned many communists overseas.  (Some, however, loyally defended the pact.) When war did break out, Stalin and Hitler divided Poland between themselves. Thus, Stalin became almost an ally of Hitler.  In 1941, however, Hitler surprised Stalin by launching a massive attack on the Soviet Union.

In the war against Hitler, the Soviet Union was now an ally of the western democracies, such as the United Kingdom, the United States, and the British Commonwealth. Many people in the west recognized that Stalin’s dictatorship was in many ways at least as bad as Hitler’s and that the alliance with the Soviet Union was merely an alliance of convenience. If and when the war against Hitler was won, tensions with the Soviets were almost inevitable.  Such tensions became especially unavoidable when, in the immediate aftermath of the war, the Soviets imposed communist dictatorships on many of the countries of eastern Europe.

Orwell, who had long been deeply suspicious of many kinds of authoritarianism, wrote Animal Farm as an allegory because openly attacking the Soviet Union might have seemed damaging to an “ally” during a time of war.  However, the allegory Orwell composed is so transparently anti-Soviet that no one could possibly misunderstand the object of his satire. The novel was not published until after the end of the war; it was rejected by several publishers who feared offending the Soviets.

Orwell thus had practical reasons for writing an allegory. However, Orwell may also have felt that writing the book as an allegory would make it more interesting to read than another dry political tract would have been.  All the charges made against the Soviet Union in Animal Farm were well-known charges and could easily have been expressed again in yet another essay.  By writing the book as an allegorical novel, Orwell made old charges seem fresh and clever.

Orwell himself wrote that he merely hoped to find a publisher who

(a) has got some paper and (b) isn't in the arms of Stalin. The latter is important. This book is murder from the Communist point of view, though no names are mentioned.

One look at the dates for George Orwell's life and the country in which he lived tell us much of the reason behind the author's choice to write Animal Farm as an allegory.

Orwell, a British citizen, lived during the first half of the twentieth century, from 1903-1950. Thus, Orwell lived through both World War I and World War II. Ironically, in 1936 and 1937, Orwell had been in Spain during their civil war and had fought on the side of the communist-backed Republican governement (although Orwell fought more because of his dislike of the Fascists than any love for communism).

Given Orwell's experience in Spain, plus his experience living through the two World Wars, in which his fellow Britons were actually allies of the Russians, it seems clear that Orwell could not openly criticize the Russians without putting himself in some peril. In fact, George Orwell is not the author's real name, but rather Eric Arthur Blair. Additionally, in an apparent effort to put further distance between himself and blatant criticism of the Russians, Orwell's original title for the novella was Animal Farm: A Fairy Story.

Furthermore, when we consider that Orwell started writing Animal Farm in 1943, at the height of World War II, the author's need to employ allegory becomes more apparent (the novella was finally published in August 1945). Thus, to protect himself and his family, it seems necessary for Orwell to publish such a novella as an allegory.