The year is 2753 (or thereabouts), and after the Martian Invasions of 1898, 1932 and 1953, the majority of Earth was plunged into a Dark Age of plagues and petty despots. But after a hundred years of civilization building back up, mankind is now stretching out into space. This journey has been through a great many troubles of course. Wars between nations, skirmishes with Martian holdouts (and allies) as well as lots and lots of politics and economic struggles. But now, after all of this, mankind and allies is looking forward.
Technology is that of the interbellum era, which covers the time between the end of World War I and the start of World War II (TL 5-6). So Automobiles, mechanical calculators, telegraph, (telephones for the rich), radio, records, BOOKS, machine guns, railroads (subways included), airships, airplanes, biochemistry, etc, etc. All with the added bonus of Selenite and Martian derived hypertech, fuels and know-how. So spaceships, death rays and advanced power sources mixed with coal and gas powered gadgets and simple computer for a "deiselpunk" feel.
Culturally the world is all about Art Deco, Burlesque, Gangsters, Jazz, Raygun Gothic, Ragtime, and Noir. Despite the troubles looming on the horizon (and right next door), people are optimistic and energetic. Add to this crushing poverty, restrictive government and alien invasion.
The Planets are not as hostile to life as they are in our universe, though they are still dangerous. Mars has a breathable atmosphere, though thin and very dry, and Venus is a sweltering jungle (cross Tarzans Jungle with Skull Island and you get the idea). Of course this means that other things live there too...
The Earth has been devestated by the repeated wars with the Sarmak Martians, and in battles between its own nations. These days, most people on Earth live in HUGE megalopolis cities. These super-cities are absolutley enormous. The lower classes live in subterranean dwellings, and the middle and upper classes living in skyscrapers and largely communal accommodations. Moving walkways interconnect the city, with fast air-travel and superhighways available between cities. Governments as we know them are unknown of, with Mega-Corporations representing governments.
Generally speaking, most of Earth is peaceful and prosperous; many old political rivalries have now moved to the new frontier of space, others are now mainly economic. Naturally there are still dangers; China and parts of Africa are unsafe for anyone who appears to be wealthy or foreign.
In cities public transport uses subways, robo-buses and robo-taxis; monorails and rockets are used for most long distance travel. There are even a few ocean liners left, though their appeal is romanticism and nostalgia, not speed. For the wealthy, gyros were at one time the "must-have" status symbol, but as the price of basic models fall they are becoming more common for the merely well-to-do who need to commute long distances, since they can be flown without a full pilot's license. Most modern cities have flight lanes and landing pads for them.
The landscape of much of Earth will be farms, or wilderness. And much wilderness is choked with the Martian Red Weed. Farmers are constantly fighting off this invasive plant as well as mutated vermin. Still some small towns and communities do exist, but are either corporate holdings or petty warlords and squatter/survivalists.
The White Council (The Sleeper Awakes and A Story of the Days to Come): A fascist cadre of technocratic Utopians. These guys rule, but keep mostly to the shadows of Mega Corporations and political puppets. They enforce the law with their G-Men and their Beast-Men (ala Island of Dr Moreau) goons. These guys are the power behind the throne, and don't normally get pushy. But they are a pain when they take notice. They are dogmatic in pursuit of "thought criminals" that are a threat. The White Council holds the secret for Cavorite and many other Martian technologies secret.
Colonies: A number of colonies exist on Mars the Moon, and Venus many founded by Mega Corporations, existing as city-states. These colonies are often all that remains of what we would see as Americana. Most were built atop the ruins of Aurorean cities, but rebuilt for human and Selenite use. These colonies are pretty Wild West in their ruggedness though a few have achieved a Casablanca like elegance. Some of the older colonies were started in the 1920s and so are well established.
Sarmak Martians (War of The Worlds): The Sarmak Martians are the Invaders that brought so much calamity to Earth in 1898-1901, 1932-1953. These creatures live primarily in the Nodus Gordii region of Mars and are greatly feared by the other peoples of the Red Planet. Some of the aliens have made alliances with human groups, even going so far as creating human/Sarmak hybrids called the Star-Begotten. The Sarmak have a foothold in the South Seas of Earth, the South Pole and are presently working on the conquest of Venus.
Selenites (The First Men in The Moon): The Selenites are the sapient insectoid inhabitants of the Earth's moon and many asteroids. They are vaguely similar to quasi-humanoid ants, about five feet tall. These creatures are all natural Monarchic Socialists, having a completely communal existance, but are stratified socially and biologically. The Grand Lunar officially allied with the White Council against the Martians, however that doesn't mean that all is friendly. Comparable to dealings with Saudi Arabia during WWII (tension and misunderstandings galore).
More to come!