The Victoria & Albert Museum in London is holding an exhibition of Modernism until July 2006.  It's in quite a small space and liable to get really crowded at peak times, but is well worth seeing. If you can't get along, or live in a different country, do have a quick peek at their website which even has a 'build your own modernist poster' facility with the best efforts showcased on the site!

Modernism took many forms from Cubo-Futurism to Bauhaus, but has two identifying characteristics
1. Things will be better in the future
2. Technology will deliver us to this utopian future

It arose out of consideration of the pointless waste of human life that was the First World War and the alternative posited by the Russian revolution.  There was a very compelling rationale for making things better - the alternative was truly too horrible to contemplate returning to. This striving for a utopian future is entirely understandable, albeit naive and starry-eyed with the benefit of hindsight.  With memories of the charnelhouse of war still fresh,  such blind faith in the irreversible evolution of mankind and protective power of technology is entirely understandable in a period of rapid technological innovation and widespread diffusion of what had previously been luxuries thanks to new methods of mass production.  The future was going to be great and it was just around the corner.  There was an avant-garde who were prepared to shout about it.  Moreover such optimism wasn't restricted to artists and dreamers.  Industrial design became part of the new aesthetic. Better housing for the people; better furniture and fittings to put in them as well as uplifting art on the walls.  The V&A analyse it under the following headings:

Searching for utopia
The very core of the modernist idea is that old ways had to be completely rethought.  The Russian revolution provided a model for an alternative society. The First World War led to a clamoring for a better society, which in turn ascribed more importance to design and art.  Cubism and Expressionism had emerged tentatively before the war, but now the process was taken off the painter's canvas and set out in brick and metal by architects and engineers.

The rise of the machine
Unlike the dystopian vision of machinery set out in Terminator and Matrix movie franchises, modernists saw mechanisation as being a desirable development. Mass production techniques advocated by FW 'Speedy' Taylor and Henry Ford were transforming ordinary domestic lives for the better - from the spread of electric light to later waves of cars, washing machines and refrigerators. Machines, these transforming agents were seen as items of unadorned beauty and purity of purpose. Form follows function, as the Bauhaus insisted.

Performing modernism
Obviously, it wasn't going to be long before the mimes got into the act. Seriously though, there was a cross-pollination between the performing arts.  Artists such as Ivan Bilibin,  Georges Braque and Pablo Picasso worked as set designers for Diaghilev's Ballet Russes.  Theatre drew heavily on the emerging industrial arts and sciences and gave them flair in return.  Admittedly, there was a certain amount of dressing up in robot costumes.

Building utopia
As the post-war generation of graduates established themselves in positions as architects and town planners, they were able to bring to life the new dynamic whether in the luxury mansions designed by Frank Lloyd Wright and leCorbusier or the new estates for the masses resulting from slum clearances in the urban centres. Unlike previous movements, modernism actually took physical shape. Ready-mixed concrete had never been so popular.

New aesthetic furniture
People spend a lot of time around their furniture. Bringing the New Design to the people, a number of industrial designers such as Marcel Breuer, Eileen Gray and Mart Stam revolutionised the design of furniture. It started with the chrome and black leather cantilevered creations of the Bauhaus and ended with the mass-produced hard plastic stackable chairs you spent primary school sitting on.

Healthy body culture
The 1930s were when naturism emerged from the, ermm, closet and into the mainstream.  Concern for health was an understandable reaction to the post-war flu epidemic. Modern buildings should have modern facilities for modern people. Mens sana in corpore sano.

National modernisms
With its association with the new and the ideal, modernism was co-opted by the ascendant right wing totalitarian political movements, taking it far from its left wing origins.  Association with extreme politics was to sound the death-knell of modernism in its European home.  At the same time, the rise of fascism led to a diaspora of talent from central Europe, leading to a transmission of ideas to the UK and more importantly to the United States where it found a second life idealising the American Dream in the 1950s.