Who was the main proponent of "the american system"?

Henry Clay

Congressman Henry Clay was the plan's foremost proponent and the first to refer to it as the "American System".

the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.