Modernism started in Western countries around 1890s.
Modernists believe that the traditional way of art, literature and even daily life become outdated; they wanted to sweep them aside.
Modernists called to re-examine the all the aspect of existence. There is no restriction for the areas for re-examination. It touches all the things, like architecture, medicine, economics, philosophy, literature etc.,
Modernists strongly believed that the traditional way and romanticism in every aspect of the life is main reason for the obstacle in progress.
In essence, the modernist movement argued that the new realities of the industrial and mechanized age were permanent and imminent, and that people should adapt their world view to accept that the new equaled the good, the true and the beautiful.
In Literature, the main theme modernism is to use free verse and reach the reality in the writing.
Tamil literature has more than 2000 years of history. All these 2000 years it has the literatures with grammatical construction.
Modernism entered in to Tamil literature almost half the century later. My assumption is the struggle for Indian freedom is the main reason for this delay. Free verse of writing tried successfully by Mahakavi Barathiyar in Tamil. He tried the different ways in his writing style. It seems most of the people accepted the way he wrote.