Because of the colonization and vietnam's power structure
Explanation:
Conflict between south and north Vietnam occurred as a result of ideological battle between democracy and Communism. At that time, the soviet union managed to spread the influence of communism on North Vietnam. United States hoped that it can formed an alliance with the South in order to prevent further spread of Communism in South East Asia.
But, western countries have the history of exploiting Vietnamese people for labors during the colonization Era. This made the rulers in south Vietnam thought that the effort to make an alliance was only a ploy for United States to obtain control over the country. This made aligning with the south Vietnam government difficult for many to accept.
