Why the Guomindang despite its attempts to unite the country failed ?

The Guomindang’s social base was in urban areas. Industrial growth was slow and limited. In cities such as Shanghai, which became the centres of modern growth, by 1919 an industrial working class had appeared numbering 500,000. Of these, however, only a small percentage were employed in modern industries such as shipbuilding.
Most were 'petty urbanites' (xiao shimin), traders and shopkeepers. Urban workers, particularly women, earned very low wages. Working hours were long and conditions of work bad.

The Guomindang despite its attempts to unite the country failed because of its narrow social base and limited political vision. A major plank in Sun Yat-Sen's programme - regulating capital and equalising land was never carried out because the party ignored the peasantry and the rising social inequalities.
It sought to impose military order rather then address the problems faced by the people.