In the end of 19th century and the beginning of the 20th century the "Modernist Movement" started in the Arts as a reaction against Realism and what was considered conservative values of that. It was not an exactly return to Romanticism but was, anyway, a look to "abstract" and to what was supposed to be "new".
Eric Hobsbawm has a concept that the 20th century , in true, started in 1914, with the First World War.
After the Second World War some movements that intended to "surpass" the "Modern" appeared.
So, between 1914 and 1945 there were not too much time for "modern"...
And the Futurism of that days was maybe a kind of "modernism" that latter walked together with dictatorial ideas... If it was so, Dadaism, that claimed to be against the principles that leaded to War, was, in some level, influenced by Futurism?
In the middle of all that, how was Surrealism and Expressionism situated?
Was Dadaism already a kind of Postmodern Movement?
Maybe Modern and Postmodern was intertwined in 20th century...