The interwar years were the crucible of Modernism, a movement fundamentally about rejecting the past and fervently seeking new ways of creating and understanding life. 

The Great War may be considered the actual beginning of the 20th century. The historical caesura marked the end of one era and the beginning of another. 
The first two decades of the 20th century indeed fall into Victorian times in that they upheld the same values, lifestyles, and mindsets. That society embraced Enlightenment ideas of rationality and progress, and despite its growing anxieties, it was essentially an optimistic society. 
All of this changed after the Great War, leading to a new way of living, thinking, and feeling. Pessimism became very strong, accompanied by a feeling that society was entering a new phase that nobody knew how to navigate. People lost faith in the old values but had a hard time finding new ones after such a catastrophe as the Great War. This led to a general feeling that life was pointless and meaningless.

It was a pervasive feeling, but it manifested most prominently in the arts, where artists actively repudiated the artistic principles of the past. No longer was it about an ‘objective’ representation of life, but rather a deeply personal interpretation and a scathing critique of the society that had allowed a cataclysmic conflict like WWI to occur.  

This new feeling eventually received the name of Modernism. 
It was never a style but a feeling, a concept, a mindset that gathered under its umbrella many different artistic styles. 

Here are a few of the most influential.

Expressionism

Born at the end of the 19th century, Expressionism was probably the older of the Artistic Vanguards. It proposed a form of art that didn’t depict reality how it was (or even the impression of reality, as Impressionism proposed, and to which Expressionism directly opposed), but rather an intentionally distorted reality that would shock the watcher/reader into looking for deeper meanings and truths. 

Expressionism criticised everything new, like industrialisation, urbanisation, and mass production, as something that society accepted without thought because it was how life was. It tried to make people think and, therefore, choose. 

Cubism

This was also an early movement that started in the first decade of the 20th century.

Cubism tried to deconstruct objects and figures by denying the two-dimensionality of visual arts and proposing to see objects from different perspectives simultaneously. 

This, of course, created fragmentation and confusion. But it was also an invitation to see the object of the piece of art from different angles, all of which were presented and equally important, in this way destroying the idea of one privileged viewpoint. 

Futurism

Contemporary to Cubism was Futurism, an Italian movement that aimed to capture in art the dynamism and energy of the modern world, which they saw as positive and powerful. 

Like all other Vanguards, Futurism proposed a caesura with the past, but it did so in a particularly vehement way, probably because the artistic past of Italy was exceptionally dominant and oppressive. 

Futurism celebrated movement, fast pace, technology and all forms of mechanisation. 

Dadaism 

Born in Switzerland during the Great War, the Dada movement was a direct reaction to that madness and senseless bloodshed. 

It intentionally made art that confused the viewers (it was predominantly visual art), even shocking and outraging them in an utterly unconventional way. 

Dada relied heavily on nonsense and the absurd. It also rejected the traditional ways of making art – painting, sculpture, etc – and rather relied on what already existed to create a new language. Dadaists used collage and what they called ‘automatic writing’ where words would come to them spontaneously, without a usual logic. 

Surrealism

In many respects, Surrealism was an evolution of Dadaism. 

This art form relied, in particular, on the subconscious, also leaning on theories from scientists like Sigmund Freud. Oniric visions are very common in this movement. 

The Surrealists believed the rational mind repressed the power of the imagination, allowing taboos to become extremely relevant to people. Instead, they proposed a balance between rationality and the power of the unconscious and dreams. 

Bauhaus

This was an extremely influential, though very short-lived, movement that arose in Germany in the interwar years. It was predominantly a design, architectural, and visual art movement. Like the contemporary Art Deco, the Bauhaus proposed that art should be used in everyday life and, in fact, almost always mixed with crafts. It rejected ornaments and focused on a very clean, stylised design. 

The Bauhaus School, which was the core of the movement, was also very actively involved in politics and social life. 

RESOURCES

V&A – What Was Modernism?
Britannica – Modernism
Khan Academy – A Lost Generation
My Modern MET – Bauhaus: How the Avant-Garde Movement Transformed Modern Art
Tate – Futurism
Tate – Cubism
Useum – Expressionism
The Art Story – Surrealism
The Dali – Dadaism
The Collector – What Is Dadaism and Where Did it Start?