As the steampunk trope gained the attention of the masses every kind of retro-futurism was labeled as "Steampunk" and most people don't know or care about the emerging "Dieselpunk" genre, often considered some variant of either Steampunk or Cyberpunk.
Dieselpunk however differs both in timeline and themes from Steampunk, the only overlapping being the First World War era.
The war created a cleavage between the era of National revolutions and romanticism, of progressive improvement of human life through science and expansion of European Western Civilization and the following era, characterized by totalitarian systems and mass communication, technological, systematic destruction of human soul and body and the last stand of a declining Europe crushed between his New World offspring and the emerging Asiatic masses. As the war itself includes both the end of the former era and the beginning of the latter, its imagery is often claimed by both genres.
Some of the human types decline and change after the war. The Second International, discredited because of the active part Socialist parties had in supporting the war effort, is abandoned and the ideals give way to a violent clash between a real or supposed "red front" who wants to "do as in Russia" and Right-wing militias; masses have been taught how to practice organized violence during the Great War and the individual who wants to make the difference must join them or learn to guide them; the bohemian artist becomes a party leader or a "Wattman", the new Elite of technology enthusiasts, addicted to speed, the cry of tortured engines on overdrive and the smell of cordite and gasoline.
In the meantime the United States, their manifest destiny to go west fulfilled and disgusted by European bloodthirsty ideals, enter the Golden Age of Jazz, an era of entertainment, sexual liberation and organized crime; posses and desperados fade away and in the cities foreign gangs threaten the rule of the law. Relatively new products such as soap bars and cigarettes make living in close-knit city communities easier and only those who "speak easy" can sink their problems in amber whiskey, prohibited by those laws whose purpose is to protect the new half of electorate from domestic violence.
Japan is no longer the battlefield for the last traditional Bushi as the new Tenno, head of a modern industrial power is eager to demonstrate to a white world their new found power and their self-proclaimed right to rule Asia.
The state of the hidden, occult world also changes; electricity is no longer enough to bring dead back to life and ectoplasmic manifestations of gauze are not capable of scaring those who saw the Hell on Earth of the Weltkrieg. The Old Ones are the new, unspeakable source of power and those who can survive reading the Necronomicon are granted the vision of new, alien realities and of a future where Nyarlathotep cries to the audient void.
The obscure, improvised rituals to contact daemonic worlds and their inhabitants now give way to better organised societies and the black mass finds a more defined form in Alister Crowley's works. A society where God is Dead seeks its roots reinventing Pagan traditions.
Meanwhile, the Ahnenerbe organization leads the way of the most obscure researches in occultism and exploitation of forbidden knowledge for totalitarian purposes: in a totalitarian state, there's no place for the lunatic mad scientist and its subhuman minions.
|Clothes||Top hats, tailcoats, corsets, John B.s, bowler hats, waistcoats, etc.||Fedoras, pinstriped suits, cloche hats, newsboy caps, zoot-suits, bomber jackets, however you would describe Iowa's outfit in Kantai Collection, etc.|
|Power sources||Coal and clockwork; coal can be replaced with anything that can be used to boil water, but coal is most associated with the times||Petoleum-based fuels; occasionally, nuclear power is involved too|
|Ideological Conflicts||Monarchy vs Democracy||Fascism vs Democracy, Capitalism vs Socialism|
|Materials||Brass, gold, copper, bronze, wood, steel||Steel, wrought iron, aluminum, chrome, polymers (like Bakelite)|
|Weapons||Repeating rifles (typically lever-action or revolving, but some bolt-actions are out there), revolvers (typically cap-and-ball revolvers), some self-loading pistols (like a Borchardt C-93 or a Bergmann No. 1), hand-cranked machine guns||Bolt-action and self-loading rifles, SMGs (typically Thompson- or MP40-based), self-loading pistols (commonly-used ones include the M1911, FN 1910, Mauser C96, and Luger P08), revolvers (usually snub-nosed ones), some early assault rifles (like the M2 Carbine, StG44, and AKM); lever-action and revolving rifles can show up, but are rare|
|Ground-based vehicles||Horses, stagecoaches, early cars and velocipedes, trains, possibly tanks in the style of The Land Ironclads, etc.||Cars, buses, velocipedes, trams, trains, tanks (possibly up to and including land dreadnoughts), etc.|
|Aircraft||Hot-air balloons, airships (typically dirigibles), maybe the occasional early aeroplane||Airships (typically blimps, semi-rigids, and Zeppelins), aeroplanes (typically WWII-era monoplanes, but some works prefer WWI-style aircraft, and some prefer the jet planes of the late 1940s and early 1950s), helicopters (rare, but still sometimes used)|
|Ships||Steamers, ironclads, liners, etc.||Dreadnoughts, destroyers, aircraft carriers, etc.; the "floating fortresses" mentioned in Nineteen Eighty-Four come to mind|