Earthman come home by James Blish (American, 1952)

Summary:
After the economic depression of the 1920's, major cities left planet Earth by means of spindizzy technology. These floating cities, commonly known as ‘okies’, have a specialization of their own: while a city focuses on agriculture, another devotes itself merely to metal extraction, and so on. Each city wanders through space searching for work. When a city encounters a planet or even another city, the leaders of each party communicate and decide if there can be an exchange of goods. If an agreement is reached, both groups prepare and sign a contract, without which the Okie might be labelled as a ‘blindestiff’ or criminal. As more and more cities flee from Earth, the crisis eventually follows them to the stars. As work and sustenance became more difficult to acquire, more and more okies go rogue, turning into space pirates. Once the news reaches Earth, police is dispatched to deal with the blindestiffs. However, thanks to the roaming nature of okies, Earth police has been unable to locate all lawbreaker cities and end the problem once and for all. As a result, the relationship between Earth and its former cities has grown tense throughout the years, the police wary of each and every okie they come across. 
 Thanks to the anti-agathy drugs that prevent aging, John Amalfi has remained the Mayor of New York City for several hundred years now. Desperate to secure the survival of his city, Amalfi has resorted to cunningness, half promises, and dubious deals. When New York reaches the planet Utopia, Amalfi makes a contract with its people only to appear to betray them to the alien Hruntians. As his siding with the Hruntians in their war against Utopia is understood as a breached contract, New York is now under persecution. In an attempt to get rid of their pursuers, Amalfi and the city manager Mark Hazleton agree to head towards the Rift, an area in which many cities have disappeared without leaving a trace. 
 The travel through the Rift takes around a hundred years but at the other end the New Yorkers find the long lost planet of He under attack by a blindestiff. The city lands on the planet and arranges a new contract with them, promising to get rid of the jungle that prevents He from having good weather. Amalfi plugs himself to the City Fathers, the super computer each Okie has, and asks them to solve He’s problem to which they suggest to regularise the planet’s axis. Amalfi resolves to use the spindizzies to tip He in the correct position but also lends the Hevians manpower to defeat the blindestiff. However, New York cannot collect its payment for the spindizzies and sends He on its way at a higher speed than thought. 
 Another couple hundred years pass before New York finds another planet, this one called Murphy. Murphy turns out to be in the vicinity of the Jungle, a congregation of poor okies under the rule of King Buda-Pesht, who instigates all the reunited cities to march to Earth and demand justice and wealth or take them through violence. 
 New York continues to travel through space although the spindizzy in Street 23 will shortly stop working. Desperate and hopeless, the okie makes one final landing on a planet in the Magellanic Cloud, where they discover a new kind of men held as slaves by the ruling elite. Because Amalfi has lived for so long, he recognises the masters of the planet as the Mad Dogs, the very first okie citizens that went rogue and the worst of them all, since they profited from enslaving sentient alien forms back in planet Thor V a long time ago. Once Earth caught word of their atrocious deeds, the city disappeared after travelling through the Rift. Amalfi manages to agree to a new contract with “the Proctors” as the slavers call themselves now in an effort to hide their past. Amalfi plots to steal the planet away from the Proctors and decides the first step is to educate the slaves in order to turn them against their masters. Since the Mad Dogs asked for the New Yorkers to repair their spindizzies as payment, Amalfi now knows the outlaw city is at the top of a temple, passing as the room in which the Proctors gather to deliberate and to govern. Amalfi realises that the Mad Dogs suspect him and his colleagues of having learned who they really are to the extent that they are preparing to obliterate New York once it takes off. Aware of this threat, Amalfi allows himself to be lead to the temple under feeble excuses on the day the city’s contract expires and, after being entertained there for a while, the Proctors reveal they planned to prevent the city from going before the contract expired so as to get rid of New York for “trespassing.” However, Amalfi went to the Temple armed with a biological weapon, with which he threatens the Proctors and manages to exit the lower levels unharmed while trapping the masters in the bowels of the building. The Mayor then proceeds to the top floor and initiates the departure sequence just as the planet’s security system informs him that the Earth police has arrived. Since the Mad Dogs have escaped and made their way to the higher levels of the temple, Amalfi taunts them to their okie by revealing he has set in motion the take off. Frantic to stop the process, the Mad Dogs rush to the control panel of their city but they are far too late and the city goes into space with all slavers on board. Once it reaches outer space, the okie is destroyed by the police, who thought it to be New York, the city they were actually pursuing. Once they have gotten rid of the dangerous rogues, the New Yorkers settle down in this new planet, completely free of worries.

Another summary:
More than three thousand years have passed since the last cosmopolitan city left the earth as a starship due to the lack of resources on the planet. That city is New York and, in the story, it is the home of AS John Amalfi and his crew, who are in search of an earth-like planet to live in. While looking for a new home, they get into trouble with the earth police because they find themselves in the middle of a war between two planets. After that, they settle down in another planet and they start working there under poor conditions because of the wide economical depression. Amalfi begins a protest against Earth to demand a better enviroment when he discovers an old enemy has infiltrated his march. But he destroys it. At the end of that fight, the earth police think that he destroyed the planet to rebel and they ban him and his crew from the galaxy. Outside the galaxy, Amalfi finds another planet with an army ruling over their ignorant society, so he decides to make the earth police believe it is them. The earth police believes it. They destroy the other society and Amalfi and his crew are able to stay there.

Another summary:
Humanity has begun to travel through space, driven by a mysterious conflict that shakes planet Earth, the most important cities of Earth evacuate their people in big spaceships. Those spaceships are outcasts because they are vagrant ships that travel from planet to planet searching for work through the different human colonies. This freedom of transit made them the main objective of the Earth police because they could become criminals.
 The story takes place in a spaceship called New York, which is looking for work, this ship has some technological advancements such as the "spindizzy" (space engine) and the anti-aging drugs (the oldest is 117 years old). 
 The mayor of the city, John Amalfi, and the ship's captain, Mark Hazleton, reached a pair of planets, which were at war and began to establish contact. At first they worked for one side, and then for the other, but they got in trouble with the Earth police. Forced to flee through the empty crevasse, they witness the destruction of many cities because of the secret of a trip without fuel, when Amalfi stops on the only planet he can find in the Rift to replenish his supplies, he has to fight against the bindlestiff (an avalanche of aliens that were the dominant species before the human race began to travel through space), which were already there.
 Later, New York settles on a planet under repair, but discovers that its currency has lost most of its value due to the worst economic downturn throughout the galaxy. A large number of cities have already gathered in a jungle, taking jobs at low prices to survive. Amalfi triggers a march protest to Earth to demand better working conditions, whose real purpose is to create a detour so that his city or population? can leave without being stopped by the police.
 However, the police believe that they have destroyed another city, forcing New York to abandon the Milky Way galaxy completely and settle in the satellite galaxy of the Large Magellanic Cloud, but the planet they choose already has an infamous city (IMT) in residence; nonetheless, Amalfi has a plan: when IMT summons the police, Amalfi sabotages the other city to get up without control; the police confuse him with New York trying to flee and destroy him. When New York City no longer fits for space, residents settle on the planet. Earth is not a place, it is an idea.

World view: The world portrayed in the story is an hypothetical society which seems to be worse than the one the author lives in.
Future projections: It’s a fearful prediction of the possible outcomes of today’s actions. Thus, it warns us against the terrible disasters (e.g. overpopulation, war, climate change) which would follow if there is no change in direction.
Ideology: The majority is oppressed by a ruling elite or an individual powergroup that come to dominate society to their own interests.
Characters, plot and writing style: The story features a rebellion against the adverse circumstances (revolutionaries may exploit newer technologies for these ends).
Classification: Dystopia